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.
Synonyms
malfunction, go wrong, be defective, be faulty
informal be on the blink, be on the fritz
1.1(Of a person) misbehave.
Synonyms
misbehave, behave badly, be up to mischief, become unruly
See parent entry: act

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