acted up; acting up; acts up
1
: to act in a way different from that which is normal or expected: such as
a
: to behave in an unruly, recalcitrant, or capricious manner
The children were acting up.
b
: show off
c
: to function improperly
This keyboard is acting up again.
2
: to become active or acute after being quiescent
Her rheumatism started to act up.
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Examples of act up in a Sentence
Verb
the two-year-old was acting up in church so much that her dad had to take her outside
you should have seen the boys acting up when they put on their aprons
Recent Examples on the Web
Gary Bedore, Kansas City Star, 7 Dec. 2025
But if your transmission acts up or your steering system goes haywire, car insurance won't help you.
—Alora Bopray, USA Today, 5 Dec. 2025
Its general sensibility seems more Superstore than The Office, down to the interstitial montages of customers acting up in the perpetually overcrowded waiting room.
—Angie Han, HollywoodReporter, 13 Oct. 2025
Sturm said his back started acting up after the team’s first practice.
—Michael Russo, New York Times, 1 Oct. 2025
See All Example Sentences for act up
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Verb
And of course, Peterson not playing would have made some wonder if the McDonald’s All-American’s hamstring had acted up again.
—Gary Bedore, Kansas City Star, 7 Dec. 2025
But if your transmission acts up or your steering system goes haywire, car insurance won't help you.
—Alora Bopray, USA Today, 5 Dec. 2025
Its general sensibility seems more Superstore than The Office, down to the interstitial montages of customers acting up in the perpetually overcrowded waiting room.
—Angie Han, HollywoodReporter, 13 Oct. 2025
Sturm said his back started acting up after the team’s first practice.
—Michael Russo, New York Times, 1 Oct. 2025
See All Example Sentences for act up
Cite this Entry
“Act up.” Merriam-Webster.com Dictionary, Merriam-Webster, https://www.merriam-webster.com/dictionary/act%20up. Accessed 16 Dec. 2025.
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