acted up; acting up; acts up
Definition of act up
(Entry 1 of 2)
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
ACT UP
abbreviation\ ˈakt-ˈəp 
\
\Definition of ACT UP (Entry 2 of 2)
AIDS Coalition to Unleash Power
Keep scrolling for more
Keep scrolling for more
Comments on act up
What made you want to look up act up? Please tell us where you read or heard it (including the quote, if possible).
Test Your Vocabulary
Slippery Words Quiz—Changing with the Times
- What is an earlier meaning of nice?
Test your knowledge - and maybe learn something along the way.
TAKE THE QUIZ
A daily challenge for crossword fanatics.
TAKE THE QUIZLove words? Need even more definitions?
Merriam-Webster unabridgedWords at Play
Ask the Editors
Word Games
- Slippery Words Quiz—Changing with the Times
Do you know these earlier meanings of words?
Take the quiz - Words of Snow and Ice Quiz
A selection of words from the chillier parts of t...
Take the quiz - True or False?
Test your knowledge - and maybe learn something a...
Take the quiz - Word Winder's CrossWinder Play the game
Share act up
Time Traveler for act up
The first known use of act up was in 1879
See more words from the same year