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 typewriter is acting up again
2
: to become active or acute after being quiescent
her rheumatism started to act up
AIDS Coalition to Unleash Power
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
Michael Russo, New York Times, 1 Oct. 2025
In the cold and austere German winter (a far cry from Dakar’s physical and cultural warmth), an anxious Nourou acts up outside a hotel and is accosted by a Polish security guard, setting off a minor chain reaction in which Maja intervenes on his behalf, much to his chagrin.
—Siddhant Adlakha, Variety, 28 Sep. 2025
Mature parents do not slap their children across the face for acting up.
—Jeanne Phillips, Mercury News, 25 Sep. 2025
Then the engine started acting up, which would have cost up to $10,000 to fix.
—Shannon Pettypiece, NBC news, 22 Sep. 2025
See All Example Sentences for act up
Examples are automatically compiled from online sources to
show current usage.
Read More
Opinions expressed in the examples do not represent those of Merriam-Webster or its editors.
Send us feedback.
Verb
Sturm said his back started acting up after the team’s first practice.
—Michael Russo, New York Times, 1 Oct. 2025
In the cold and austere German winter (a far cry from Dakar’s physical and cultural warmth), an anxious Nourou acts up outside a hotel and is accosted by a Polish security guard, setting off a minor chain reaction in which Maja intervenes on his behalf, much to his chagrin.
—Siddhant Adlakha, Variety, 28 Sep. 2025
Mature parents do not slap their children across the face for acting up.
—Jeanne Phillips, Mercury News, 25 Sep. 2025
Then the engine started acting up, which would have cost up to $10,000 to fix.
—Shannon Pettypiece, NBC news, 22 Sep. 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 6 Oct. 2025.
Copy CitationLove words? Need even more definitions?
Merriam-Webster unabridged
Share