noun, plural ac·tiv·i·ties.

  1. 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.
  2. a specific deed, action, function, or sphere of action: social activities.
  3. work, especially in elementary grades at school, that involves direct experience by the student rather than textbook study.
  4. energetic activity; animation; liveliness.
  5. a use of energy or force; an active movement or operation.
  6. normal mental or bodily power, function, or process.
  7. Physical Chemistry. the capacity of a substance to react, corrected for the loss of reactivity due to the interaction of its constituents.
  8. Physics.
    1. the number of atoms of a radioactive substance that disintegrate per unit of time, usually expressed in curies.
    2. radioactivity.
  9. an organizational unit or the function it performs.

noun plural -ties

  1. the state or quality of being active
  2. lively action or movement
  3. any specific deed, action, pursuit, etcrecreational activities
  4. the number of disintegrations of a radioactive substance in a given unit of time, usually expressed in curies or disintegrations per second
    1. the capacity of a substance to undergo chemical change
    2. the effective concentration of a substance in a chemical system. The absolute activity of a substance B, λ B, is defined as exp (μ B RT) where μ B is the chemical potential

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.


  1. A physiological process.
  2. The presence of neurogenic electrical energy in electroencephalography.
  3. An ideal concentration for which the law of mass action will apply perfectly.
  4. The intensity of a radioactive source.
  5. The ability to take part in a chemical reaction.
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