act up Meaning in the Cambridge English Dictionary
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Meaning of “act up” in the English Dictionary

"act up" in British English

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act up

phrasal verb with act uk   us   /ækt/ verb
If a ​person, ​especially a ​child, ​acts up, they ​behavebadly: Sophie got ​bored and ​startedacting up. If a ​machine or ​part of the ​bodyacts up, it does not ​perform as well as it should: My ​car always ​acts up in ​coldweather. Her ​shoulder was ​acting up (= ​hurting because of ​injury).
(Definition of act up from the Cambridge Advanced Learner’s Dictionary & Thesaurus © Cambridge University Press)

"act up" in American English

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act up

phrasal verb with act  us   /ækt/ verb

act up (BEHAVE BADLY)

to ​behavebadly: The little ​girl was acting up, so her ​mother took her out of the ​restaurant.

act up

phrasal verb with act  us   /ækt/ verb

act up (OPERATE BADLY)

to ​operatebadly: My ​car is acting up again - I don't ​know what's ​wrong with it.

act up

phrasal verb with act  us   /ækt/ verb

act up (BECOME ACTIVE)

to ​becomeactive: Her ​allergies acted up when she went ​hiking in the ​woods.
(Definition of act up from the Cambridge Academic Content Dictionary © Cambridge University Press)
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