Merriam-Webster Logo
SINCE 1828
Menu
×

An Encyclopædia Britannica Company

act up

verb

Definition of act up

  1. intransitive verb

  2. 1 :  to act in a way different from that which is normal or expected: such asa :  to behave in an unruly, recalcitrant, or capricious manner the children were acting upb :  show offc :  to function improperly this typewriter is acting up again

  3. 2 :  to become active or acute after being quiescent her rheumatism started to act up

See act up defined for kids

Indulge Your Inner Word Nerd

emoji-the-quiz
The Emoji Quiz
video-title-words-of-the-year-1066
Words of the Year: 1066
image386126722
Words That Come From the Dinner Table
alt-59721dd897313
The 'Best' Way to Sign Off On An E-mail

Examples of act up in a Sentence

  1. the two-year-old was acting up in church so much that her dad had to take her outside

  2. you should have seen the boys acting up when they put on their aprons

First Known Use of act up

1879

act up Synonyms

Synonyms
act out, misbehave, carry on
Related Words
misconduct; disobey, rebel; clown (around), cut up, fool around, horse around, kid (around); show off; roughhouse
Near Antonyms
obey; acquit, act, bear, comport, conduct, demean, deport, quit; comply, conform; check, collect, compose, constrain, contain, control, curb, handle, inhibit, move, quiet, repress, restrain

ACT UP

abbreviation

Definition of ACT UP

  1. AIDS Coalition to Unleash Power

Learn More about act up

  1. See words that rhyme with act up Thesaurus: All synonyms and antonyms for act up

Seen and Heard

What made you want to look up act up? Please tell us where you read or heard it (including the quote, if possible).

show hide

Love words? Need even more definitions?

Subscribe to America's largest dictionary and get thousands more definitions and advanced search—ad free!

WORD OF THE DAY

haphazard

play

marked by lack of plan or order

Get Word of the Day daily email!

TRENDING NOW

  1. scaramouch A new White House communications director

  2. non sequitur “It does not follow”

  3. admiral's mast A massive search ends with an 'admiral's mast'.

  4. calumny 'An untrue statement that is made to damage someone's reputation'

  5. kakistocracy Frustrated Twitter users have been searching for this word.

SEE ALL

BROWSE DICTIONARY

act up

Test Your Vocabulary

The Emoji Quiz

  • emoji-the-quiz
  • What phase of the moon is this: 🌖 ?
Spell It

Can you spell these 10 commonly misspelled words?

TAKE THE QUIZ
Word Winder's CrossWinder

Test Your Knowledge - and learn some interesting things along the way.

TAKE THE QUIZ

Love words? Need even more definitions?

Subscribe to America's largest dictionary and get thousands more definitions and advanced search—ad free!

Words at Play

alt-59721dd897313
The 'Best' Way to Sign Off On An E-mail

Give them your best

image386126722
Words and Phrases That Come from the Dinner Table

Fill your plate with these surprising food words

ghost-being-disinvited-from-party
'Disinvite' or 'Uninvite'?

A disinvited guest is an uninvited problem

alt-596f730ceb5ae
Words We're Watching: 'Scoby'

Kombucha lovers unite.

Ask the Editors

video-title-words-of-the-year-1066
Words of the Year: 1066

Or, Why Pig Meat is Called 'Pork' and Cow Meat is Called 'Beef'

payday
How Often Is 'Biweekly'?

Don't get us started on 'bimonthly'

video-irregardless-grammar-peeve-blend-of-the-synonyms-irrespective-and-regardless
Irregardless

It is in fact a real word (but that doesn't mean you should use it).

video-moose-goose-weird-plurals
Weird Plurals

One goose, two geese. One moose, two... moose. What's up with that?

Word Games

emoji-the-quiz
The Emoji Quiz

Think you’re an emoji 👓 expert? Let’s see 🤔

Take the quiz
image941935269
A Game of Thrones Word Quiz

In the Game of Thrones quiz, you learn some new vocabulary. (It’s quite safe, really. You will not die.)

Take the quiz
Spell It
Spell It

Can you spell these 10 commonly misspelled words?

Take the quiz
Word Winder's CrossWinder
Word Winder's CrossWinder

A game of winding words.

Play the game
Examples: act up in a Sentence