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.
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
Clara Harter, Los Angeles Times, 28 Mar. 2026
Intel’s representative explained that the Intel team has pushed this to extremes in testing—their vPro team even challenged each other, successfully, to try to access a troubled machine that was acting up on a flight, over airplane Wi-Fi!
—John Burek, PC Magazine, 25 Mar. 2026
Bruce, as the stunt shark built to menace them is nicknamed, is acting up and delaying the acting itself.
—Christopher Smith, Oc Register, 10 Mar. 2026
Meanwhile, the guests, who have literally just arrived five minutes ago, are already acting up.
—Rafaela Bassili, Vulture, 10 Mar. 2026
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
The black flies are not the only troublesome creature acting up during the unseasonably warm weather.
—Clara Harter, Los Angeles Times, 28 Mar. 2026
Intel’s representative explained that the Intel team has pushed this to extremes in testing—their vPro team even challenged each other, successfully, to try to access a troubled machine that was acting up on a flight, over airplane Wi-Fi!
—John Burek, PC Magazine, 25 Mar. 2026
Bruce, as the stunt shark built to menace them is nicknamed, is acting up and delaying the acting itself.
—Christopher Smith, Oc Register, 10 Mar. 2026
Meanwhile, the guests, who have literally just arrived five minutes ago, are already acting up.
—Rafaela Bassili, Vulture, 10 Mar. 2026
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 3 Apr. 2026.
Copy CitationLove words? Need even more definitions?
Merriam-Webster unabridged
