act - definition and synonyms


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present tense
present participleacting
past tenseacted
past participleacted
  1. 1
    [intransitive] to do something for a particular reason or in a particular way
    act in good faith (=believe that you are acting honestly):

    We acted in good faith – we did not know the goods were stolen.

    act out of necessity/desperation/love/compassion/curiosity etc:

    She claims that she acted out of necessity (=because she had to).

     Synonyms and related words
    1. a.
      to do something immediately, especially in order to deal with an urgent problem

      Had the paramedics not acted so swiftly, he would have died.

      act to do something:

      We must act now to prevent further damage to our rainforests.

  2. 2
    [intransitive] if you act for someone, you do something as their representative
    act for:

    Lawyers acting for the family will issue a statement this morning.

  3. 3
    [intransitive] to behave in a particular way, especially a way that is unusual or annoying
    act like:

    I’ve acted like a total idiot.

    act suspiciously/strangely:

    A man was seen acting suspiciously twenty minutes before the robbery.

    act as if:

    Just act as if nothing’s happened.

    1. a.
      to behave in a particular way by doing something
      act reasonably/fairly/illegally/responsibly/dishonestly etc:

      Did the BBC act reasonably in sacking the journalist?

      The court must establish whether the accused acted illegally.

  4. 4
    [intransitive] to start to have an effect

    Don’t expect the medicine to act immediately.

    act on:

    The experiment should show us how sugars act on the enamel of the teeth.

     Synonyms and related words
  5. 5
    [intransitive/transitive] to perform in plays or films

    I’ve always wanted to act.

    act the part/role (of someone/something):

    Philip Schofield acted the part of Joseph.

     Synonyms and related words