act up
Britishverb
-
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.
“That’s not the idea. The idea is to have them clean their act up so that they do better and the stock goes up and their dividends go up,” Ryan said.
From Seattle Times • Feb. 26, 2024
In her four-star review Midgley suggested the show occasionally "feels scripted", noting the Furys know that "the cameras are on them and perhaps act up for them".
From BBC • Aug. 18, 2023
“You ain’t stoppin’ what’s goin’ on with me sweetheart,” Palmer lip-synced.“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 • Aug. 16, 2023
My granddaughters get upset, act up and give her a hard time, and I can understand why.
From Washington Post • Aug. 31, 2022
As we settled into our seats for a late-night flight to Paris, my stomach began to act up.
From "Mountains Beyond Mountains" by Tracy Kidder and Michael French
![]()
Definitions and idiom definitions from Dictionary.com Unabridged, based on the Random House Unabridged Dictionary, © Random House, Inc. 2023
Idioms from The American Heritage® Idioms Dictionary copyright © 2002, 2001, 1995 by Houghton Mifflin Harcourt Publishing Company. Published by Houghton Mifflin Harcourt Publishing Company.