activity

from The American Heritage® Dictionary of the English Language, 5th Edition.

• noun The state of being active.
• noun Energetic action or movement; liveliness.
• noun A specified pursuit in which a person partakes.
• noun An educational process or procedure intended to stimulate learning through actual experience.
• noun The intensity of a radioactive source.
• noun The ability to take part in a chemical reaction.
• noun A physiological process.

from The Century Dictionary.

• noun The state of action; doing.
• noun Activeness; the quality of acting promptly and energetically.
• noun An exercise of energy or force; an active movement or operation; a mode or course of action.
• noun In physical, a term introduced by Sir William Thomson as an equivalent of “rate of doing work,” or the rate per unit of time at which energy is given out by a working system.
• noun A physical or gymnastic exercise; an agile performance.
• noun In. psychology, a self-determination of mental process, experienced or inferred, especially characteristic of the conative consciousness.

from the GNU version of the Collaborative International Dictionary of English.

• noun The state or quality of being active; nimbleness; agility; vigorous action or operation; energy; active force.

from Wiktionary, Creative Commons Attribution/Share-Alike License.

• noun The state or quality of being active; nimbleness; agility; vigorous action or operation; energy; active force; as, an increasing variety of human activities.
• noun something done as an action or a movement
• noun something done for pleasure or entertainment, especially one involving movement or an excursion.
• noun Use (of internet, playstation, bank account etc.)

from WordNet 3.0 Copyright 2006 by Princeton University. All rights reserved.

• noun a process existing in or produced by nature (rather than by the intent of human beings)
• noun an organic process that takes place in the body
• noun the state of being active
• noun the trait of being active; moving or acting rapidly and energetically
• noun (chemistry) the capacity of a substance to take part in a chemical reaction
• noun any specific behavior