Definition of act verb from the Oxford Advanced American Dictionary

Oxford3000

act

verb
/ækt/
 
 

do something

1 [intransitive] to do something for a particular purpose or in order to deal with a situationIt is vital that we act to stop the destruction of the rainforests.The girl's life was saved because the doctors acted so promptly.He claims he acted in self-defense.

behave

2 [intransitive] to behave in a particular way + adverbJohn's been acting very strangely lately. act like someone/somethingStop acting like spoiled children! act as if/though…She was acting as if she'd seen a ghost.help In spoken English people often use like instead of as if or as though in this meaning: She was acting like she'd seen a ghost.

pretend

3 [intransitive] to pretend by your behavior to be a particular type of person + adjectiveI decided to act dumb.He acts all macho, but he's a real softie underneath.

perform in play/movie

4 [intransitive, transitive] to perform a part in a play or movieHave you ever acted?Most of the cast act well. act somethingWho's acting (= taking the part of) Hamlet?The play was well acted.

perform function

5 [intransitive] to perform a particular role or function act as somethingCan you act as interpreter?A five-year sentence should act as a deterrent to others. act like somethinghormones in the brain that act like natural painkillers

have effect

6 [intransitive] act (on something) to have an effect on somethingAlcohol acts quickly on the brain.It took a few minutes for the drug to act.
IDIOMS

act/play the fool

to behave in a stupid way in order to make people laugh, especially in a way that may also annoy them
Quit playing the fool and get to work!act the foolplay the fool

be/act your age

to behave in a way that is suitable for someone of your age and not as though you were much younger
Isn't it time you started acting your age?be your ageact your age

behave/act as if you own the place

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think you own the place

(disapproving) to behave in a very confident way that annoys other people, for example by telling them what to dobehave as if you own the placeact as if you own the place
PHRASAL VERBS

act for/on behalf of someone

to be employed to deal with someone's affairs for them, for example by representing them in courtact for behalf ofact on behalf of

act on/upon something

to take action as a result of advice, information, etc.Acting on information from a member of the public, the police raided the club.Why didn't you act on her suggestion?act onact upon

act somethingout

1 to perform a ceremony or show how something happened, as if performing a playThe ritual of the party convention is acted out in the same way every year.The children started to act out the whole incident.2 to act a part in a real situationShe acted out the role of the wronged lover.act out

act up

(informal)1 to behave badlyThe kids started acting up.2 to not work as it shouldHow long has your ankle been acting up?act up