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List of words for Letter 'A'
Click on to hear the word and definition.
abiotic factor A nonliving part of an ecosystem.
absorption The disappearance of a sound wave into a surface.
abyssal plain The vast flat lands beyond the continental shelf that cover almost half of the deep ocean floor.
acceleration Change in velocity with respect to time.
acid A substance that tastes sour and turns blue litmus paper red.
acid rain Moisture that falls to Earth after being mixed with wastes from burned fossil fuels.
acidity The strength of an acid.
action The force one object applies to a second, as in Newton’s third law of motion, which states, "For every action, there is an equal but opposite reaction." See reaction.
adaptation A characteristic that enables a living thing to survive in its environment.
aerial root A root that never touches the ground but can take in moisture from the air.
aerosol A type of colloid in which liquid drops or solid particles are spread throughout a gas.
air mass A large region of the atmosphere where the air has similar properties throughout.
air pressure The force put on a given area by the weight of the air above it.
alkalinity The strength of a base.
alternative energy source A source of energy other than the burning of a fossil fuel.
amphibian A vertebrate that lives part of its life in water and part of its life on land.
anemometer A device that measures wind speed.
aneroid barometer A spring enclosed in a pleated metal can that expands or contracts to indicate changes in air pressure.
angiosperm A seed plant that produces flowers. See gymnosperm.
aquifer An underground layer of rock or soil filled with water.
asexual reproduction The production of a new organism from only one cell.
asteroid Minor planet. One of many small, rocky objects that orbit the Sun between the orbits of Mars and Jupiter.
asteroid belt Region between Mars and Jupiter where most asteroids are found.
atmosphere The blanket of gases that surrounds Earth.
atom The smallest unit of an element that retains the properties of that element. See molecule.
aurora The northern or southern lights that appear in the night sky, especially in polar regions.
