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

a heroic act.

the process of doing

caught in the act.

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.

an instrument or document stating something done or transacted.

one of the main divisions of a play or opera

the second act of Hamlet.

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

the personnel of such a group

The act broke up after 30 years.

false show; pretense; feint

The politician's pious remarks were all an act.

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.

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

He acted promptly in the emergency.

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

I am required to act before noon tomorrow.

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

to act as manager.

to produce an effect; perform a function

The medicine failed to act.

to behave or conduct oneself in a particular fashion

to act well under all conditions.

to pretend; feign

Act interested even if you're bored.

to perform as an actor

He acted in three plays by Molière.

to be capable of being performed

His plays don't act well.

to serve or substitute (usually fol. by for )

In my absence the assistant manager will act for me.

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

to act Macbeth.

to feign; counterfeit

to act outraged virtue.

to behave as

He acted the fool.

Obsolete . to actuate. ?

act on or 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.

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.

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, esp. after a period of improvement or remission

My arthritis is acting up again this morning.

get or 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.

act funny

to display eccentric or suspicious behavior.

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.

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.

verb

act out , carry on , raise hell , rebel , sow one’s wild oats , act