Random Science Words With a Plain Definition Under a Cover

Five random science words a press, each with a plain definition under a cover to guess first.

exoskeleton
mass
state of matter
bacteria
food chain

Next step Draw one of the 118 elements Draw a planet

How it works

These random science words come from school science: life science, earth and space, physics and chemistry. Say what a term means, then tap its cover to read a short definition in plain words.

Read the full guide

Quiz yourself or a class

Press Pick 5 new science words. Explain each term aloud, then tap Show definition to check. For a drawing, acting or guessing round, give one player the words and let the others guess from the clues.

Narrow it down

The Branch list under the button keeps the draw to life science, earth and space, physics or chemistry. More filters, its last entry, opens the Level row (elementary, middle school, high school) and Starts with. The levels are our own grading, not a curriculum.

Tips

Draw two terms and say how they are linked: predator and prey, solute and solvent, crust and mantle.
Stuck on a definition? Say what the thing is not: an asteroid is not a comet.

Questions and answers

What grade are these science words for?

The Level row sorts them into elementary, middle school and high school. The grading is ours, by where a term is usually first met, and follows no state standards and no textbook.

Where do the definitions come from?

We wrote each one in plain words, then checked it against the term's Wiktionary entry and the opening of its Wikipedia article. A term stays only when both back the definition.

Can I use the words for a classroom game?

Yes. Draw five for a quick quiz, a guessing game or a word wall. Each press deals new terms, and the Branch list keeps them to the unit you are teaching.

Does the list include the chemical elements?

No. It holds terms such as atom, isotope and noble gas; the 118 elements have a page of their own.

All 306 science words

Life science 93

adaptation A change or a feature that fits a living thing to its environment.
algae Simple photosynthetic organisms, such as seaweed, that are not land plants.
allele One of the alternative forms of the same gene at a given location on a chromosome.
amphibian An animal, such as a frog, that starts life in water and can later live on land.
antibody A protein the immune system makes to find and bind to a germ or other invader.
artery A blood vessel that carries blood away from the heart.
bacteria Tiny organisms made of one cell with no nucleus.
biodiversity The variety of plant and animal life in a region or on Earth.
biome A large region of the world with its own climate, plants and animals, such as a desert.
blood The red liquid that the heart pumps around the body, carrying oxygen.
bone One of the hard parts that make up the skeleton.
brain The organ inside the head that controls the body and does the thinking.
camouflage Colors or shapes that help an animal blend in so it is hard to see.
carnivore An animal that eats other animals.

Show all 306 science words (292 more)

Life science, continued

cell The smallest unit of a living thing; every plant and animal is made of them.
cell membrane The thin layer that surrounds a cell and controls what passes in and out.
chlorophyll The green pigment in plants that takes in light for photosynthesis.
chloroplast The structure in a plant cell where photosynthesis takes place.
chromosome A package of DNA and proteins in a cell that carries genes.
decomposer A living thing, such as a fungus, that breaks down dead plants and animals.
digestion The breaking down of food into substances the body can absorb.
DNA The molecule that carries the genetic instructions of a living thing.
ecosystem The living things of a place together with their environment, working as one system.
enzyme A protein that speeds up a chemical reaction in a living thing.
eukaryote A living thing whose cells have a nucleus.
evolution The change in the inherited traits of living things over many generations.
exoskeleton A hard outer covering that supports and protects an animal such as an insect or a crab.
extinction The dying out of a species: it becomes extinct at the death of its last member.
food chain The feeding links from a plant to the animal that eats it, and on to the animal that eats that one.
food web All the connected food chains of an ecosystem, showing what eats what.
fruit The part of a plant that holds its seeds.
fungus An organism of the kingdom that includes mushrooms, molds and yeasts.
gene A unit of heredity, a stretch of DNA passed from parent to offspring.
genotype The genetic makeup of an organism: the set of genes it carries.
germination The moment a seed begins to sprout and grow.
gill The organ a fish uses to take oxygen from water.
habitat The place where a species naturally lives, with what it needs to survive.
heart The organ that pumps blood around the body.
herbivore An animal that eats only plants.
heredity The passing of traits from parents to their offspring.
hibernation A deep sleep-like state in which some animals spend the winter.
homeostasis The way a body keeps its inner conditions, such as temperature, steady.
hormone A signaling substance made in one tissue and carried to another, where it acts.
insect A small animal with six legs and a body in three parts.
invertebrate An animal with no backbone, such as an insect, a worm or a snail.
larva The young form of an insect or other animal before it changes into an adult.
leaf A flat part that grows from a plant's stem and captures sunlight to make food.
life cycle The stages a living thing passes through from its start to the time it has young.
lung One of the two organs in the chest used for breathing.
mammal An animal with hair or fur that feeds its young with milk.
meiosis Cell division that makes sex cells with half the usual number of chromosomes.
metamorphosis A change of body form as an animal grows, as when a caterpillar becomes a butterfly.
migration The seasonal journey of animals from one region to another.
mitochondrion A structure in a cell that releases energy from food.
mitosis Cell division that gives two new cells with the same chromosomes as the first.
muscle A body tissue that can tighten and relax to make a part of the body move.
mutation A change in the DNA of a living thing.
natural selection The process by which inherited traits that help survival and reproduction become more common.
nectar The sweet liquid that flowers make and that bees and butterflies drink.
neuron A nerve cell, which carries electrical signals through the body.
nucleus The part of a cell that holds its DNA; also the center of an atom.
omnivore An animal that eats both plants and animals.
organ A part of an organism, made of tissues, that carries out one function, such as the heart.
organism Any living thing: a plant, an animal, a fungus or a single cell.
osmosis The movement of water through a membrane toward the side with more dissolved matter.
parasite A living thing that lives on or in another and feeds at its expense.
petal One of the showy leaf-like parts that surround the center of a flower.
phenotype The traits of a living thing that can be observed.
phloem The plant tissue that carries sugars from the leaves to the rest of the plant.
photosynthesis The way green plants use sunlight to make food from water and carbon dioxide.
plankton Tiny living things that drift in the sea or in fresh water.
pollen A fine dust from the male part of a flower, needed before seeds can form.
pollination The carrying of pollen to a flower so that it can make seeds.
population All the living things of one species in one area.
predator An animal that hunts and eats other animals.
prey An animal that another animal, its predator, kills and eats.
prokaryote An organism whose cells have no nucleus, such as a bacterium.
protein A large molecule made of chains of amino acids, found in every living cell.
reptile A cold-blooded animal with scaly skin, such as a snake, a lizard or a turtle.
ribosome A tiny structure in a cell where proteins are made.
root The organ that anchors a plant in the soil and absorbs water and minerals.
seed A plant's small package of a young plant and stored food, from which a new one grows.
skeleton The frame of bones that supports the body of an animal.
species A group of living things of the same kind that can breed with one another.
spore A cell for reproduction, released by a fungus, a fern or a moss, that can grow into a new one.
stem The stalk that carries a plant's leaves, flowers and fruit and moves water up from the roots.
symbiosis A close, long-term relationship between two different species.
taxonomy The science of naming living things and sorting them into groups.
tissue A group of similar cells that work together in a body.
trait A characteristic of a living thing, such as eye color, that can be passed on.
vein A blood vessel that carries blood toward the heart.
vertebrate An animal with a backbone.
xylem The plant tissue that carries water up from the roots.

Earth and space 82

aquifer An underground layer of rock or sand that holds water.
asteroid A small rocky body that orbits the Sun.
atmosphere The layer of gases that surrounds a planet.
aurora Bands of colored light in the night sky near the poles.
Big Bang The theory that the universe expanded from a very hot, dense beginning.
black hole A region of space where gravity is so strong that not even light can escape.
canyon A deep valley with steep sides, often cut by a river.
carbon cycle The cycle in which carbon is exchanged between the atmosphere, the oceans, the ground and living things.
cave A natural hollow space under the ground or in the side of a hill.
climate The pattern of weather that a region has over a long period.
cloud A visible mass of tiny water droplets or ice crystals hanging in the atmosphere.
comet A small icy body that grows a glowing tail when it passes near the Sun.
condensation The change of a gas into a liquid, as when water drops form on a cold glass.
constellation A group of stars that forms a pattern in the night sky.
crust The solid outermost layer of a planet such as the Earth.
delta Land built up from sediment where a river flows into a sea or a lake.
desert A barren, dry area of land where very little rain falls.
drought A period of unusually low rainfall.
earthquake A sudden shaking of the Earth's surface as energy is released underground.
eclipse The hiding of one body in space by another, as when the Moon covers the Sun.
epicenter The point on the surface directly above the place where an earthquake starts.
equator The imaginary line around the middle of the Earth, halfway between the poles.
erosion The wearing away of rock and soil by water, wind or ice.
evaporation The change of a liquid into a gas at its surface, as when a puddle dries.
exoplanet A planet outside our solar system.
fault A break in the Earth's crust along which the rock on each side has moved.
fossil The preserved remains or trace of an animal or plant that lived in a past age.
fossil fuel A fuel, such as coal, oil or natural gas, formed from the remains of ancient living things.
galaxy An enormous collection of stars with gas and dust, bound together by gravity.
geyser A spring that now and then erupts, sending hot water and steam upward.
glacier A body of dense ice, built up from snow over many years, that moves slowly under its own weight.
greenhouse effect The warming of a planet when gases in its atmosphere trap heat.
groundwater Water held under the ground in soil and in cracks in rock.
hemisphere Half of the Earth, such as the half north of the equator.
humidity The amount of water vapor in the air.
hurricane A large spinning storm with very strong winds that forms over warm ocean water.
igneous rock Rock formed when magma or lava cools and hardens.
jet stream A narrow current of fast-moving air high in the atmosphere.
latitude Distance north or south of the equator, measured in degrees.
lava Molten rock that flows out of a volcano onto the surface.
light-year The distance light travels in one year, a unit for the distances between stars.
lightning A flash of light made by a discharge of electricity in a cloud or between a cloud and the ground.
lithosphere The rigid outer shell of the Earth: the crust and the top of the mantle.
longitude Distance east or west of the prime meridian, measured in degrees.
magma Molten rock beneath the surface of the Earth.
mantle The thick layer of the Earth between its crust and its core.
metamorphic rock Rock changed by great heat or pressure.
meteor The glowing trail seen when a small body from space heats up as it falls through the atmosphere.
meteorite The remains of a meteoroid: a rock from space that has fallen to a planet's surface.
mineral A solid substance found in nature that was never alive, such as quartz or salt.
nebula A cloud of gas and dust in space.
nitrogen cycle The movement of nitrogen between the air, the soil and living things.
orbit The path an object in space follows as it circles another, such as a planet around a star.
ozone layer A layer high in the atmosphere that absorbs most of the Sun's ultraviolet rays.
permafrost Ground that stays frozen for two or more years in a row.
planet A large, rounded body in space that travels around a star.
plate tectonics The theory that the Earth's outer shell is broken into large plates that slowly move.
precipitation Water that falls from clouds as rain, snow, sleet or hail.
rainbow A band of colors across the sky, formed when raindrops bend and reflect sunlight.
redshift The stretching of light toward longer, redder wavelengths, as from a galaxy moving away.
satellite A body, natural or made by people, that orbits a planet.
season One of the parts of the year, such as spring or winter, marked by its weather.
sediment Small bits of rock, sand or mud carried and laid down by water, wind or ice.
sedimentary rock Rock formed from layers of sediment pressed together.
seismic wave A wave of energy that travels through the Earth, as from an earthquake.
soil The mixture of minerals and organic matter on the surface of the ground in which plants grow.
solar system The Sun together with the planets and other bodies that orbit it.
star A massive, glowing ball of plasma held together by its own gravity, such as the Sun.
stratosphere The layer of the atmosphere above the troposphere; it holds the ozone layer.
subduction The sinking of one tectonic plate beneath another.
supernova The powerful explosion of a star.
telescope An instrument that makes distant objects, such as planets, look nearer and larger.
thunder The sound caused by lightning.
tide The rise and fall of sea level caused by the gravity of the Moon and the Sun.
tornado A rotating funnel of air that touches both the ground and the cloud above it.
troposphere The lowest layer of the atmosphere, where almost all weather happens.
tsunami A series of huge sea waves, often caused by an earthquake under the ocean.
volcano A vent in the crust of a planet from which molten rock, ash and gases erupt.
water cycle The cycle in which water evaporates from the oceans, condenses and falls again as precipitation.
weather The state of the air at a place and time: hot or cold, wet or dry, calm or windy.
weathering The breaking down of rock where it stands by weather, water and living things.
wind The natural movement of air from one place to another.

Physics 72

absolute zero The lowest possible temperature, zero on the Kelvin scale.
acceleration The rate at which velocity changes.
amplitude The maximum size of a wave or vibration, measured from its middle value.
battery A device that stores energy in chemical cells and supplies it as electric power.
buoyancy The upward force of a liquid or a gas on an object placed in it.
centripetal force The force that keeps an object moving in a circle, pointing toward the center.
conduction The passing of heat or electricity through a material.
conductor A material that lets heat or electricity pass through it easily.
convection The carrying of heat by the movement of a liquid or a gas.
density The mass of a substance in each unit of its volume.
diffraction The spreading of a wave as it passes an edge or goes through a narrow gap.
Doppler effect The change in the frequency of a wave when its source moves toward or away from you.
echo A sound heard again after it bounces off a surface.
electric current A flow of electric charge, measured in amperes.
electricity The set of effects caused by electric charge, at rest or in motion.
electromagnet A magnet made by passing an electric current through a coil of wire.
electromagnetic spectrum The whole range of electromagnetic waves, from radio waves to gamma rays.
energy The capacity to do work or to bring about change.
entropy A measure of the disorder of a system.
force A push or a pull on an object.
frequency The number of waves or vibrations in one second.
friction The force that resists one surface sliding or rolling over another.
gravity The force that pulls objects toward one another, and toward the Earth.
heat Energy that passes from a hotter thing to a colder one.
inclined plane A flat sloping surface, such as a ramp, used to raise a load with less force.
inertia The tendency of an object to stay at rest or stay in motion unless a force changes that.
insulator A material that does not let heat or electricity pass through it easily.
joule The unit of energy and of work.
kinetic energy The energy an object has because it is moving.
lens A curved piece of glass or plastic that bends light to focus or spread it.
lever A simple machine: a stiff bar that pivots on a point called the fulcrum.
light The form of energy that the eye can see.
magnet An object that attracts iron and makes a magnetic field.
magnetic field The region around a magnet where its force acts.
mass The quantity of matter in an object.
momentum The mass of a moving object multiplied by its velocity.
motion A change in the position of an object over time.
newton The unit of force.
nuclear fission The splitting of the nucleus of an atom into smaller nuclei, with a release of energy.
nuclear fusion The joining of two light atomic nuclei into a heavier one, with a release of energy.
photon A particle of light.
potential energy Stored energy that an object has because of its position or condition.
power The rate at which work is done or energy is used.
pressure The force on a surface divided by the area it presses on.
prism A transparent block that splits white light into its colors.
pulley A wheel with a rope or belt around it, used to lift a load or change the direction of a pull.
radiation Energy that travels as waves or particles, such as light or heat from the Sun.
radioactive decay The process by which an unstable atomic nucleus loses energy by giving off radiation.
reflection The bouncing of light or sound off a surface.
refraction The bending of a wave, such as light, as it passes from one material into another.
resistance A measure of how much an object opposes the flow of electric current; its unit is the ohm.
resonance A large vibration set up when something is pushed at its own natural frequency.
scalar A quantity that has magnitude (size) but no direction.
semiconductor A material that conducts electricity better than an insulator but less well than a metal.
shadow The dark shape formed behind an object that stands in the way of light.
simple machine A basic device, such as a lever or a pulley, that changes the size or direction of a force.
sound Vibrations that travel through air or another material and can be heard.
speed How fast something moves: the distance it covers in a given time.
temperature A number that tells how hot or cold something is, read from a thermometer.
thermodynamics The branch of physics that deals with heat, work and energy.
thermometer An instrument that measures temperature.
torque The turning effect of a force.
vector A quantity that has both a size and a direction.
velocity Speed in a given direction.
vibration An oscillation: a rapid motion back and forth about a rest position.
voltage The difference in electric potential between two points, measured in volts; it drives a current.
watt The unit of power: one joule each second.
wave A disturbance that carries energy from one place to another.
wavelength The distance from one crest of a wave to the next.
wedge A simple machine with a thick end and a thin edge, used to split things apart.
weight The force of gravity on an object.
wheel and axle A simple machine: a wheel fixed to a rod so that the two turn together.

Chemistry 59

acid A substance that can give a proton to another; its solution in water has a pH below 7.
activation energy The least energy needed to start a chemical reaction.
alkali metal One of a group of soft, very reactive metals that includes sodium and potassium.
alloy A mixture of a metal with one or more other elements, such as steel.
atom The smallest unit of a chemical element.
atomic number The number of protons in the nucleus of an atom.
base A substance with a pH above 7; it can neutralize an acid.
boiling The rapid change of a liquid into a gas, with bubbles forming inside the liquid.
catalyst A substance that speeds up a chemical reaction without being used up.
chemical bond The force that holds atoms together in a molecule or a crystal.
chemical reaction A process in which substances change into different substances.
combustion Burning: a chemical reaction with oxygen that gives off heat and light.
compound A substance made of two or more elements chemically joined.
concentration The amount of a substance in a given amount of a mixture.
corrosion The slow wearing away of a metal by chemical reaction with its surroundings.
covalent bond A chemical bond in which atoms share pairs of electrons.
crystal A solid in which the atoms sit in an ordered pattern that repeats in every direction.
electrolysis The use of an electric current to drive a chemical change.
electrolyte A substance that conducts electricity when dissolved in water or melted.
electron A tiny particle with a negative charge.
element A pure substance made of only one kind of atom.
endothermic Taking in heat, as a chemical reaction can.
exothermic Giving off heat, as a chemical reaction can.
freezing The change of a liquid into a solid when it is cooled.
gas A state of matter with no fixed shape that spreads out to fill its container.
half-life The time it takes for half of a quantity, such as a radioactive substance, to decay.
halogen One of a group of reactive elements that includes fluorine, chlorine and iodine.
hydrocarbon A compound made only of hydrogen and carbon.
ion An atom or a molecule that carries an electric charge.
ionic bond A chemical bond formed by the attraction between ions of opposite charge.
isotope One of the forms of an element whose atoms have different numbers of neutrons.
liquid A state of matter that flows and takes the shape of its container.
mass number The total number of protons and neutrons in the nucleus of an atom.
matter Anything that has mass and takes up space.
melting The change of a solid into a liquid when it is heated.
metal A material, such as iron or copper, that is usually shiny and conducts heat and electricity.
mixture A material produced by mixing two or more substances that do not combine chemically.
mole The unit for an amount of substance.
molecule Two or more atoms held together by chemical bonds.
neutron A particle with no charge in the nucleus of an atom.
noble gas One of the elements, such as helium and neon, that hardly react with anything.
oxidation A chemical reaction in which a substance joins with oxygen or loses electrons.
periodic table A chart of all the chemical elements arranged in rows and columns.
pH A scale that tells how acidic or basic a solution is.
physical change A change in how a substance looks or feels that makes no new substance.
plasma A state of matter made of charged particles, as in lightning and in stars.
polymer A substance made of very long molecules built from many repeating units.
proton A particle with a positive charge in the nucleus of an atom.
redox A reaction in which one substance loses electrons and another gains them.
rust The flaky red-brown oxide that forms on iron left in damp air.
solid A state of matter that keeps its own shape and volume.
solute The substance that is dissolved in a solution.
solution A mixture in which one substance is dissolved evenly in another.
solvent The substance, often a liquid, in which another substance dissolves.
state of matter One of the forms matter takes: solid, liquid, gas or plasma.
stoichiometry The working out of the amounts of substances that take part in a chemical reaction.
sublimation The change of a solid straight into a gas without becoming a liquid first.
titration A way to find the concentration of a solution by adding measured amounts of another.
valence electron An electron in the outer shell of an atom that can take part in a bond.

How this list was compiled: Terms from school science in four branches, each with a plain definition written for this page in American spelling; no textbook's, publisher's or exam body's word list was copied, and openstax.org was not read. The three levels (elementary, middle school, high school) are our own grading of where a term is usually first met; they follow no standard and no state's curriculum. Sources, fetched 2026-10-01 through the Wikimedia APIs and addressed in x.src and x.wp: the term's English Wiktionary entry (CC BY-SA 4.0) and the opening of its English Wikipedia article (CC BY-SA 4.0). Each definition was written first and then checked two ways. A script required at least one content word of the definition to stand in the entry's definition lines and at least one in the first three sentences of the article, and reported every definition that shared few words with them; the writer then read each reported definition (46 of them) beside both texts and reworded it until it said nothing the two did not. Four terms were dropped because the entry gave no definition of its own to check against (rock cycle, chemical formula, neutralization) or repeated another card (chemical change). For three terms the entry read is the main spelling or the singular (epicentre, light year, alga, bacterium), and x.src says which. After the file was written a script read it back and ran the check again. Licence: own work