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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 constituents.
Physics.

the number of atoms of a radioactive substance that disintegrate per unit of time, usually expressed in curies.
.

an organizational unit or the function it performs.
Contemporary Examples

Adam had few, if any, activities outside his home and no friends.
The Trials of Nancy Lanza Diane Dimond January 6, 2013

“They have plenty of activities, they have a very good after-school program,” says one.
De Blasio Misread His Mandate, Now Some of His Own Supporters are Fighting Back Over Charter School Cuts Conor P. Williams March 10, 2014

He traces the activities primarily of liberal, secular, and daring bloggers in the run-up to, during, and after the revolutions.
What Do Arab Millennials Want? William O’Connor June 30, 2014

Whistle, available now, offers an easy and digestible way for owners to get the most relevant info on your dog’s activities.
Fitness Gadgets … for Your Dog Megan Humphreys February 17, 2014

Remember, we do not recommend doing the activities described, except for the nap.
Why the Biathlon Makes Bonds of Us All Brett Singer February 15, 2014

Historical Examples

It was this multiplicity of activities and interests that proved fatal to him.
Encyclopaedia Britannica, 11th Edition, Volume 7, Slice 6 Various

Of Rouquet’s activities as an artist in England there are scant particulars.
De Libris: Prose and Verse Austin Dobson

activities double on themselves and tangle themselves up in other activities until each activity becomes a mystery to itself.
Gargoyles Ben Hecht

I followed him about while he arranged for the termination of the day’s activities.
Astounding Stories of Super-Science September 1930 Various

As I understand it, you had no capacity at that time to follow his activities?
Warren Commission (5 of 26): Hearings Vol. V (of 15) The President’s Commission on the Assassination of President Kennedy

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.

in schoolwork sense, 1923, American English, from activity.
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 mass action will apply perfectly.

The intensity of a radioactive source.

The ability to take part in a chemical reaction.