Definition of act up in English:

act up

1 informal (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, crash, develop a fault, go wrong, break down, give out, stall, be defective, be faulty, fail, cease to function, cease to work, stop working
informal conk out, go kaput, go phut, go on the blink, be on the blink
British informal pack up, play up
1.1Behave badly: all children talk back and act up from time to time
More example sentences
  • In his three-year-old debut at Gulfstream in January, Friends Lake acted up at the gate and ran badly in the Holy Bull, finishing third, 12 lengths behind the winner.
  • The day we visit the kindergarten is only the second time in his life that Ed acts up.
  • The teenager was asked about conversations he had with the dean at Los Angeles' John Burroughs Middle School, where the boy had a history of acting up in class.
Synonyms
misbehave, give someone trouble, cause someone trouble, act badly, get up to mischief, get up to no good, be bad, be naughty, forget oneself, misconduct oneself; clown about/around, fool about/around, act the clown, act the fool, act the goat, act foolishly
informal carry on, mess about/around
British informal muck about/around, play up
2Be promoted to a more senior position on a temporary basis.
More example sentences
  • What is the process for being put forward for promotion or acting up; your line manager can do it, or somebody you work with can do it, but somebody else has a final say?
  • When someone is acting up it takes another uniform off the street,’ he said.
  • He said: ‘There have been problems due to some staff being unwilling to act up.’
See parent entry: act

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