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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, especially 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.
physical chemistry. the capacity of a substance to react, corrected for the loss of reactivity due to the interaction of its const-tuents.
physics.

the number of atoms of a radioactive substance that disintegrate per unit of time, usually expressed in curies.
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an organizational unit or the function it performs.
noun (pl) -ties
the state or quality of being active
lively action or movement
any specific deed, action, pursuit, etc: recreational activities
the number of disintegrations of a radioactive substance in a given unit of time, usually expressed in curies or disintegrations per second

the capacity of a substance to undergo chemical change
the effective concentration of a substance in a chemical system. the absolute activity of a substance b, λb, is defined as exp (μbrt) where μb is the chemical potential

n.

c.1400, “active or secular life,” from old french activité, from medieval latin activitatem (nominative activitas), a word in scholastic philosophy, from latin activus (see active). meaning “state of being active, briskness, liveliness” recorded from 1520s; that of “capacity for acting on matter” is from 1540s.

activity ac·tiv·i·ty (āk-tĭv’ĭ-tē)
n.

a physiological process.

the presence of neurogenic electrical energy in electroencephalography..

an ideal concentration for which the law of m-ss action will apply perfectly.

the intensity of a radioactive source.

the ability to take part in a chemical reaction.