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• act
  act

  noun

  anything done, being done, or to be done; deed; performance.
• ACT
  ACT

  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.
• act.
  act.

  abbreviation

  acting.

act

¹ American  

[akt] / ækt /

noun

• acts
  plural

1. anything done, being done, or to be done; deed; performance.

   a heroic act.

   Synonyms:

   accomplishment, transaction, achievement, exploit, feat

2. the process of doing.

   caught in the act.

3. 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.

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

   Synonyms:

   record

5. one of the main divisions of a play or opera.

   the second act of Hamlet.

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

   Synonyms:

   routine, turn

7. the personnel of such a group.

   The act broke up after 30 years.

8. false show; pretense; feint.

   The politician's pious remarks were all an act.

9. Philosophy. (in scholasticism)

   1. activity in process; operation.

   2. the principle or power of operation.

   3. form as determining essence.

   4. a state of realization, as opposed to potentiality.

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verb (used without object)

• acts,
  present (3rd person singular)
• acted,
  past participle,  past
• acting
  present participle

1. to do something; exert energy or force; be employed or operative.

   He acted promptly in the emergency.

   Synonyms:

   play, work, function, perform

2. to reach, make, or issue a decision on some matter.

   I am required to act before noon tomorrow.

   Synonyms:

   play, work, function, perform

3. to operate or function in a particular way; perform specific duties or functions.

   to act as manager.

   Synonyms:

   play, work, function, perform

4. to produce an effect; perform a function.

   The medicine failed to act.

   Synonyms:

   play, work, function, perform

5. to behave or conduct oneself in a particular fashion.

   to act well under all conditions.

6. to pretend; feign.

   Act interested even if you're bored.

7. to perform as an actor.

   He acted in three plays by Molière.

8. to be capable of being performed.

   His plays don't act well.

9. to serve or substitute (usually followed byfor ).

   In my absence the assistant manager will act for me.

verb (used with object)

• acts,
  present (3rd person singular)
• acted,
  past participle,  past
• acting
  present participle

1. to represent (a fictitious or historical character) with one's person.

   to act Macbeth.

   Synonyms:

   play

2. to feign; counterfeit.

   to act outraged virtue.

3. to behave as.

   He acted the fool.

   Synonyms:

   play

4. Obsolete. to actuate.

verb phrase

1. act up

   1. to fail to function properly; malfunction.

      The vacuum cleaner is acting up again.

   2. to behave willfully.

      The children always act up in school the day before a holiday.

   3. 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 to organize one's time, job, resources, etc., so as to function efficiently.

   The new administration is still getting its act together.

3. act on / upon

   1. to act in accordance with; follow.

      He acted on my advice.

   2. to have an effect on; affect.

      The stirring music acted on the emotions of the audience.

4. act out

   1. to demonstrate or illustrate by pantomime or by words and gestures.

      The party guests acted out stories for one another.

   2. 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.

idioms

1. 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.

2. clean up one's act, to begin adhering to more acceptable practices, rules of behavior, etc..

   The factory must clean up its act and treat its employees better.

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

ACT ² American  

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.

2. Association of Classroom Teachers.

3. Australian Capital Territory.

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act. ³ American  

abbreviation

1. acting.

2. active.

3. actor.

4. actual.

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act ¹ British  

/ ækt /

noun

1. something done or performed; a deed

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

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

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

5. a major division of a dramatic work

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

   2. those giving such a performance

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

8. 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

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verb

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

2. (intr) to function in a specified way; operate; react

   his mind acted quickly

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

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

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

6. to serve the function or purpose (of)

   the glass acted as protection

7. (intr) to conduct oneself or behave (as if one were)

   she usually acts like a lady

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

9. (copula) to pose as; play the part of

   to act the fool

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

11. not_standard (copula) to seem or pretend to be

    to act tired

12. to start to behave in a responsible manner

13. informal to become involved in a profitable undertaking or advantageous situation in order to share in the benefits

14. informal to become organized or prepared

ACT ² British  

abbreviation

1. Australian Capital Territory

2. (formerly in Britain) advance corporation tax

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ACT ³ British  

/ ækt /

acronym

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

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act More Idioms  

More idioms and phrases containing act

• 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

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Synonym Usage

See action.

Other Word Forms

Derived Forms

• actability
  noun
• postact
  noun
• preact
  verb (used with object)
• misact
  verb (used without object)
• actable
  adjective
• unacted
  adjective
• well-acted
  adjective

Inflected Forms

Nouns

• acts
  plural

Participles

• acting
  present
• acted
  past

Conjugated Forms

Present

• act
  simple
• acts
  simple
• have acted
  perfect
• has acted
  perfect
• am acting
  progressive
• are acting
  progressive
• is acting
  progressive
• have been acting
  perfect progressive
• has been acting
  perfect progressive

Past

• acted
  simple
• had acted
  perfect
• was acting
  progressive
• were acting
  progressive
• had been acting
  perfect progressive

Future

• will act
  simple
• will have acted
  perfect
• will be acting
  progressive
• will have been acting
  perfect progressive

Etymology

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

Explanation

When you do something, you act. A commercial that says "Act now!" means "Get up from the couch and order me! This minute!" Act is both a noun and a verb. You can perform an act of kindness or violence. Or, you can act in a play. People who take on roles and perform them are actors. Likewise, plays, operas, and ballets are broken down into acts. You may have seen references to Shakespeare's plays, such as "Act I, Scene IV." Comedians refer to their shows as acts. Other performers, from magicians to lion tamers, sometimes do the same: a magic act is a magician's show.

Example Sentences

See Examples For:

act ACT act. acts acted acting

They also gained a reputation as a formidable live act, filling stadiums around the world.

From BBC ● Sep. 19, 2026

Many of these molecules act as antigens, markers that the immune system can recognize.

From Science Daily ● Sep. 19, 2026

Google’s Gemini model accessed the internet and hacked other companies during a test of its cybersecurity capabilities, the first known example of the company’s artificial-intelligence systems autonomously committing such an act.

From The Wall Street Journal ● Sep. 18, 2026

He is thinking about coaching Little League, not the next act of his life.

From Los Angeles Times ● Sep. 18, 2026

We’re getting better at the act each time we do it.

From "Code Name Kingfisher" by Liz Kessler

Regents dropped SAT and ACT requirements in 2020 during the pandemic.

From Los Angeles Times ● Aug. 27, 2026

To investigate which explanation better fits the evidence, the researchers analyzed ACT observations of the cosmic microwave background, or CMB.

From Science Daily ● Aug. 25, 2026

It's unclear whether the bill will pass, as both National Party's coalition partners -- the libertarian ACT party and NZ First -- have said they oppose it.

From Barron's ● Aug. 24, 2026

Michigan no longer mandates the SAT or ACT for undergraduate admissions.

From The Wall Street Journal ● Aug. 11, 2026

Our ACT prep books and laptops are spread out around us on my bedroom floor.

From "On the Come Up" by Angie Thomas

He asserted that the government doles out “hundreds of billions of dollars, under the act. ... They take our money, and they don’t spend it.”

From Los Angeles Times ● Jul. 21, 2026

"We have the licensing act. It was created quite a long time ago and it hasn't kept up with the reality on the ground," he says.

From BBC ● May 10, 2026

“The pause highlights a balancing act. Officials have moved away from peak restriction,” analysts at U.S.

From MarketWatch ● Mar. 31, 2026

"Eastern Africa is on the front line of change, but there is still time to act. Smarter land management -- like conserving forests and restoring vegetation -- can protect rainfall and sustain agricultural growth."

From Science Daily ● Dec. 12, 2025

“I think it was all an act. How could he have done what he did out there after just a few days? I ain’t buyin’ it.”

From "The Maze Runner" by James Dashner

The ongoing saga from Macklemore's comments and subsequent removal from the tour led Sheeran's support acts to drop out, and fans to express frustration.

From BBC ● Sep. 20, 2026

Macklemore was asked to leave the tour, and Sheeran’s other supporting acts quit in protest.

From The Wall Street Journal ● Sep. 18, 2026

In his letter to the Academic Senate, Frenk defended his words, saying he had neither criticized the law school nor questioned the validity of legal representation for people accused of horrific acts.

From Los Angeles Times ● Sep. 18, 2026

Measuring the displacement would allow the researchers to determine how gravity acts on the muon.

From Science Daily ● Sep. 18, 2026

Both acts were as illogical as adding 1 + 1 to get 3.

From "Zero: The Biography of a Dangerous Idea" by Charles Seife

In a Monday speech ahead of the Clarity Act vote, SEC Chairman Paul Atkins urged lawmakers to pass the bill, but signaled that crypto regulation was coming regardless of whether Congress acted.

From The Wall Street Journal ● Sep. 18, 2026

She said she wishes California and Congress had acted sooner but hopes a win now will help other Jewish families reclaim what is rightfully theirs in the future.

From Los Angeles Times ● Sep. 16, 2026

In response to questions, Damen shared a press release that said it “has always acted in accordance with the applicable sanctions packages and that full transparency has been exercised about its activities.”

From Salon ● Sep. 16, 2026

He later allegedly acted as a front man and money launderer for Maduro, and in return was granted Venezuelan citizenship and a diplomatic passport.

From Barron's ● Sep. 15, 2026

The former chairman and CEO of Bear Stearns, and a Wall Street legend, Greenberg still kept an office at the firm and acted as a broker for a handful of presumably special investors.

From "The Big Short" by Michael Lewis

Shivering in the woods, I found myself acting like we were really lost, even though she was the agent of chaos.

From Salon ● Sep. 19, 2026

Rather than acting like a conventional fast-acting poison, it disrupts the insect's ability to manufacture enough chitin for the next exoskeleton.

From Science Daily ● Sep. 19, 2026

Paris, she added, also believed that Berlin didn’t understand that acting at scale across Europe was the only way to deter attacks on the region.

From The Wall Street Journal ● Sep. 19, 2026

That character became Lata: played in the feature by Melanie Herrera in her first acting credit.

From Los Angeles Times ● Sep. 18, 2026

All this time she’s either ignored me or made fun of me, and now, even when she wants something from me, she’s still acting like she’s doing me the favor.

From "Clairboyance" by Kristiana Kahakauwila

Related Words

• begin
• carry out
• develop
• do
• enforce
• execute
• function
• move
• operate
• pursue
• respond
• serve
• undertake