act up - definition and synonyms

phrasal verb [intransitive] informal
present tense
I/you/we/theyact up
he/she/itacts up
present participleacting up
past tenseacted up
past participleacted up
  1. 1
    if children act up, they behave badly

    The kids have been acting up again.

  2. 2
    if a part of your body or a piece of equipment acts up, it starts to become painful or to develop problems

    I hope my back doesn’t start acting up again.

See also main entry: act