Definition of act up in English:

act up

  • 1(Of a thing) fail to function properly: the plane’s engine was acting up
    More example sentences
    • The laptop computer that we have been using for performing pulmonary function tests had been acting up lately, overheating and shutting itself off.
    • Then again, my body did like to pick the wrong times to start acting up.
    • I think the service is messed up here, it was acting up before the phone broke.
    malfunction, go wrong, be defective, be faulty
    informal be on the blink, be on the fritz
  • 1.1(Of a person) misbehave.
    More example sentencesSynonyms
    misbehave, behave badly, be up to mischief, become unruly
See parent entry: act

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Word of the day coloratura
Pronunciation: ˌkələrəˈto͝orə
elaborate ornamentation of a vocal melody