Definition of act up in US English:

act up

phrasal verb

  • 1(of a thing) fail to function properly.

    ‘the plane's engine was acting up’
    • ‘Their Internet connection is acting up, so I mucked about and deduced that either Shaw is having issues or stranger things are afoot, then promptly fell asleep.’
    • ‘The back still acts up now and again, but the diet at least makes it possible to swing the club - and he has lost 20 lb in weight.’
    • ‘Later I learned that he had thought I was having a problem with the gauge, which had been acting up a few weeks earlier.’
    • ‘A couple of weeks ago it started acting up: even after leaving it all night to charge, it sometimes doesn't charge at all.’
    • ‘Her right knee was acting up a bit from soccer the day before, and besides, she just didn't feel like it.’
    • ‘I reckon I covered a mile before my legs started to act up.’
    • ‘No point in fighting it, though I do think it strange that both this and the preceding two monitors started acting up within a couple of months of the end of the guarantee.’
    • ‘Alas, the desktop computer which was acting up before I'd left has now failed again.’
    • ‘My leg was acting up, painful and disobedient, but no more than it has a hundred times before.’
    • ‘The laptop computer that we have been using for performing pulmonary function tests had been acting up lately, overheating and shutting itself off.’
    • ‘‘The gearbox started acting up real early in the race, and we didn't think that we would make it,’ said Macaluso.’
    • ‘My modem is acting up so it took forever to log on, shades of things to come.’
    • ‘But the record player, which has been acting up for months now, wheezed a few breaths before officially dying.’
    • ‘My PC has been acting up badly for the past month.’
    • ‘I think the service is messed up here, it was acting up before the phone broke.’
    • ‘For instance, this morning I wanted to print some details for Mike and Joan's travel insurance and the printer started to act up, Grrrrrrrrrrrrrr.’
    • ‘Fortunately I had cut a new CD-Rom backup only the day before the system started acting up so all is not lost.’
    • ‘Then again, my body did like to pick the wrong times to start acting up.’
    • ‘A few weeks back I mentioned that the gear box in the car was acting up a bit, earlier today it went kaput.’
    • ‘I don't think psychologists have to deal with their own computers when they start to act up.’
    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
    View synonyms
    1. 1.1 (of a person) misbehave.