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.”

Example Sentences

Examples are provided to illustrate real-world usage of words in context. Any opinions expressed do not reflect the views of Dictionary.com.

See Examples For:

act up

“So if you gon’ act up, I’m ‘bouta link up, I’m ‘bouta link up, I’m ‘bouta link up.”

From Los Angeles Times ● Jul. 8, 2023

The more serious the occasion, the more he'll act up.

From BBC ● Oct. 24, 2022

Keep this smoke-and-mirrors act up, Martin St. Louis’ over-performing bunch can kiss Connor Bedard goodbye.

From Seattle Times ● Oct. 21, 2022

Lopez says she hopes to keep playing for many years, even if her knee is starting to act up a bit.

From Reuters ● Aug. 5, 2022

But then, during the first orbit, the capsule’s automatic control system began to act up, causing the capsule to pull back and forth like a badly aligned car.

From "Hidden Figures" by Margot Lee Shetterly

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