act Definition in Cambridge British English Dictionary
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Definition of "act" - British English Dictionary

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actverb

uk   us   /ækt/

act verb (BEHAVE)

[I] to behave in the stated way: Don't be so silly - you're acting like a child! He acted as if he'd never met me before.
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act verb (DO SOMETHING)

B2 [I] to do something for a particular purpose or to solve a problem: [+ to infinitive] Engineers acted quickly to repair the damaged pipes. She acted without thinking. Who is acting for/on behalf of (= who is representing) the defendant? He never acts on other people's advice (= does what other people suggest). Acting on impulse (= without thinking first) can get you into a lot of trouble.
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act verb (HAVE AN EFFECT)

[I] to have an effect: The anaesthetic acted quickly.

act verb (PERFORM)

B1 [I or T] to perform a part in a film, play, etc.: Ellis Pike was chosen to act the part of the lawyer in the film. Have you ever acted in a play before?act the fool, martyr, etc. to behave in a particular, usually bad, way: Why are you always acting the fool?
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actnoun

uk   us   /ækt/

act noun (THING DONE)

B2 [C] something that you do: an act of aggression/bravery/madness/terrorism a kind/thoughtless/selfish act The simple act of telling someone about a problem can help. Primitive people regarded storms as an act of God. artistic representations of the sexual act
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act noun (PERFORMANCE)

C2 [S] behaviour that hides your real feelings or intentions: Was she really upset or was that just an act? [C] a person or group that performs a short piece in a show, or the piece that they perform: a comedy/juggling/trapeze act Our next act is a very talented young musician.B1 [C] a part of a play or opera: Shakespeare's plays were written in five acts. The hero does not enter until the second act/Act Two.
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act noun (LAW)

[C] specialized law a law or formal decision made by a parliament or other group of people who make the laws for their country: an Act of Parliament the Betting and Gaming Act Almost two hundred suspects were detained in the UK last year under the Prevention of Terrorism Act. The state legislature passed an act banning the sale of automatic weapons.
(Definition of act from the Cambridge Advanced Learners Dictionary & Thesaurus © Cambridge University Press)
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