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English definition of “act up”

act up

verb uk phrasal verb with act   /ækt/ us  
If a person, especially a child, acts up, they behave badly: Sophie got bored and started acting up.Bad and wrong behaviourDisobedientObeying and breaking the lawObedient and compliant If a machine or part of the body acts up, it does not perform as well as it should: My car always acts up in cold weather. Her shoulder was acting up (= hurting because of injury).Not functioningPain and painful
(Definition of act up from the Cambridge Advanced Learners Dictionary & Thesaurus © Cambridge University Press)
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