Synonyms

act up

British

verb

informal (intr, adverb) to behave in a troublesome way

the engine began to act up when we were miles from anywhere

"Collins English Dictionary — Complete & Unabridged" 2012 Digital Edition © William Collins Sons & Co. Ltd. 1979, 1986 © HarperCollins Publishers 1998, 2000, 2003, 2005, 2006, 2007, 2009, 2012

act up Idioms

Misbehave. For example, With an inexperienced rider, this horse always acts up . [c. 1900]
Malfunction, as in I'm not sure what's wrong with my car, but the transmission is acting up . In both usages up means “abnormally.”

Definitions and idiom definitions from Dictionary.com Unabridged, based on the Random House Unabridged Dictionary, © Random House, Inc. 2023