/ Dictionary / Index A activity: Meaning and Definition of Find definitions for: ac•tiv•i•ty Pronunciation: (ak-tiv'i-tē), [key] — pl. -ties. the state or quality of being active: There was not much activity in the stock market today. He doesn't have enough physical activity in his life. a specific deed, action, function, or sphere of action: social activities. work, esp. in elementary grades at school, that involves direct experience by the student rather than textbook study. energetic activity; animation; liveliness. a use of energy or force; an active movement or operation. normal mental or bodily power, function, or process. the capacity of a substance to react, corrected for the loss of reactivity due to the interaction of its constituents. the number of atoms of a radioactive substance that disintegrate per unit of time, usually expressed in curies. radioactivity. an organizational unit or the function it performs. Random House Unabridged Dictionary, Copyright © 1997, by Random House, Inc., on Infoplease. See also: activity (Thesaurus) activist activize Related Content Daily Word Quiz: eccentric Analogy of the Day: Today’s Analogy Spelling Bee: Today’s Spelling Bee Frequently Misspelled Words Frequently Mispronounced Words Easily Confused Words Writing & Language