Definition of act verb from the Oxford Advanced American Dictionary

     

    act

     verb
    verb
    NAmE//ækt//
     
    Verb Forms present simple I / you / we / they act
     
    he / she / it acts
     
    past simple acted
     
    -ing form acting
     
     
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    do something
  1. 1 [intransitive] to do something for a particular purpose or in order to deal with a situation It 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.
  2. behave
  3. 2 [intransitive] to behave in a particular way + adv. John's been acting very strangely lately. act like somebody/something Stop acting like spoiled children! act as if/though… She was acting as if she'd seen a ghost. 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.
  4. pretend
  5. 3 [intransitive] to pretend by your behavior to be a particular type of person + adj. I decided to act dumb. He acts all macho, but he's a real softie underneath.
  6. perform in play/movie
  7. 4 [intransitive, transitive] to perform a part in a play or movie Have you ever acted? Most of the cast act well. act something Who's acting (= taking the part of) Hamlet? The play was well acted.
  8. perform function
  9. 5 [intransitive] to perform a particular role or function act as something Can you act as interpreter? A five-year sentence should act as a deterrent to others. act like something hormones in the brain that act like natural painkillers
  10. have effect
  11. 6[intransitive] act (on something) to have an effect on something Alcohol acts quickly on the brain. It took a few minutes for the drug to act.
  12. Idioms
    act/play the fool
     
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    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!
    be/act your age
     
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    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?
    behave/act as if you own the place,think you own the place(disapproving)
     
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    to behave in a very confident way that annoys other people, for example by telling them what to do
    Phrasal Verbsact for/on behalf of somebodyact on/upon somethingact somethingoutact up
See the Oxford Advanced Learner's Dictionary entry: act