[ akt ]
See synonyms for act on
  1. anything done, being done, or to be done; deed; performance: a heroic act.

  2. the process of doing: caught in the act.

  1. a formal decision, law, or the like, by a legislature, ruler, court, or other authority; decree or edict; statute; judgment, resolve, or award: an act of Congress.

  2. an instrument or document stating something done or transacted.

  3. one of the main divisions of a play or opera: the second act of Hamlet.

  4. a short performance by one or more entertainers, usually part of a variety show or radio or television program.

  5. the personnel of such a group: The act broke up after 30 years.

  6. false show; pretense; feint: The politician's pious remarks were all an act.

  7. Philosophy. (in scholasticism)

    • activity in process; operation.

    • the principle or power of operation.

    • form as determining essence.

    • a state of realization, as opposed to potentiality.

verb (used without object)
  1. to do something; exert energy or force; be employed or operative: He acted promptly in the emergency.

  2. to reach, make, or issue a decision on some matter: I am required to act before noon tomorrow.

  1. to operate or function in a particular way; perform specific duties or functions: to act as manager.

  2. to produce an effect; perform a function: The medicine failed to act.

  3. to behave or conduct oneself in a particular fashion: to act well under all conditions.

  4. to pretend; feign: Act interested even if you're bored.

  5. to perform as an actor: He acted in three plays by Molière.

  6. to be capable of being performed: His plays don't act well.

  7. to serve or substitute (usually followed by for): In my absence the assistant manager will act for me.

verb (used with object)
  1. to represent (a fictitious or historical character) with one's person: to act Macbeth.

  2. to feign; counterfeit: to act outraged virtue.

  1. to behave as: He acted the fool.

  2. Obsolete. to actuate.

Verb Phrases
  1. act on / upon

    • to act in accordance with; follow: He acted on my advice.

    • to have an effect on; affect: The stirring music acted on the emotions of the audience.

  2. act out,

    • to demonstrate or illustrate by pantomime or by words and gestures: The party guests acted out stories for one another.

    • Psychology. to give overt expression to (repressed emotions or impulses) without insightful understanding: The patients acted out early traumas by getting angry with the analyst.

  1. act up,

    • to fail to function properly; malfunction: The vacuum cleaner is acting up again.

    • to behave willfully: The children always act up in school the day before a holiday.

    • to become painful or troublesome, especially after a period of improvement or remission: My arthritis is acting up again this morning.

  2. get / have one's act together Informal. to organize one's time, job, resources, etc., so as to function efficiently: The new administration is still getting its act together.

Idioms about act

  1. act funny, to display eccentric or suspicious behavior.

  2. act one's age, to behave in a manner appropriate to one's maturity: We children enjoyed our uncle because he didn't always act his age.

  1. clean up one's act, Informal. to begin adhering to more acceptable practices, rules of behavior, etc.: The factory must clean up its act and treat its employees better.

Origin of act

First recorded in 1350–1400; Middle English act(e), from Middle French, from Latin ācta, plural of āctum “something done,” noun use of neuter past participle of agere “to do, drive”; also from Latin āctus “deed,” noun use of masculine past participle of agere

synonym study For act

1. See action.

Other words for act

Other words from act

  • mis·act, verb (used without object)
  • postact, noun
  • pre·act, verb (used with object)
  • un·act·ed, adjective
  • well-acted, adjective

Words Nearby act

Other definitions for ACT (2 of 3)


  1. Trademark. a standardized college admissions test developed by ACT, Inc., measuring English, mathematics, reading, and science skills: originally an abbreviation of American College Testing/American College Test.: Compare SAT.

  2. Association of Classroom Teachers.

  1. Australian Capital Territory.

Other definitions for act. (3 of 3)


  1. acting.

  2. active.

  1. actor.

  2. actual. Unabridged Based on the Random House Unabridged Dictionary, © Random House, Inc. 2023

How to use act in a sentence

British Dictionary definitions for act (1 of 3)


/ (ækt) /

  1. something done or performed; a deed

  2. the performance of some physical or mental process; action

  1. (capital when part of a name) the formally codified result of deliberation by a legislative body; a law, edict, decree, statute, etc

  2. (often plural) a formal written record of transactions, proceedings, etc, as of a society, committee, or legislative body

  3. a major division of a dramatic work

    • a short performance of skill, a comic sketch, dance, etc, esp one that is part of a programme of light entertainment

    • those giving such a performance

  4. an assumed attitude or pose, esp one intended to impress

  5. philosophy an occurrence effected by the volition of a human agent, usually opposed at least as regards its explanation to one which is causally determined: Compare event (def. 4)

  1. (intr) to do something; carry out an action

  2. (intr) to function in a specified way; operate; react: his mind acted quickly

  1. to perform (a part or role) in a play, etc

  2. (tr) to present (a play, etc) on stage

  3. (intr; usually foll by for or as) to be a substitute (for); function in place (of)

  4. (intr foll by as) to serve the function or purpose (of): the glass acted as protection

  5. (intr) to conduct oneself or behave (as if one were): she usually acts like a lady

  6. (intr) to behave in an unnatural or affected way

  7. (copula) to pose as; play the part of: to act the fool

  8. (copula) to behave in a manner appropriate to (esp in the phrase act one's age)

  9. (copula) not standard to seem or pretend to be: to act tired

  10. clean up one's act to start to behave in a responsible manner

  11. get in on the act informal to become involved in a profitable undertaking or advantageous situation in order to share in the benefits

  12. get one's act together informal to become organized or prepared

Origin of act

C14: from Latin actus a doing, performance, and actum a thing done, from the past participle of agere to do

Derived forms of act

  • actable, adjective
  • actability, noun

British Dictionary definitions for ACT (2 of 3)


abbreviation for
  1. Australian Capital Territory

  2. (formerly in Britain) advance corporation tax

British Dictionary definitions for ACT (3 of 3)


/ (ækt) /

n acronym for
  1. (in New Zealand) Association of Consumers and Taxpayers: a small political party of the right

Collins English Dictionary - Complete & Unabridged 2012 Digital Edition © William Collins Sons & Co. Ltd. 1979, 1986 © HarperCollins Publishers 1998, 2000, 2003, 2005, 2006, 2007, 2009, 2012

Other Idioms and Phrases with act


In addition to the idioms beginning with act

  • act of faith
  • act of God
  • act on
  • act one's age
  • act out
  • act up
  • act upon

also see:

  • catch in the act
  • clean up (one's act)
  • do a disappearing act
  • get in the act
  • get one's act together
  • hard (tough) act to follow
  • high-wire act
  • in the act of
  • put on an act

The American Heritage® Idioms Dictionary Copyright © 2002, 2001, 1995 by Houghton Mifflin Harcourt Publishing Company. Published by Houghton Mifflin Harcourt Publishing Company.