Cambridge Dictionaries online Cambridge Dictionaries online

The most popular online dictionary and thesaurus for learners of English

English definition of “act up”

act up

verb phrasal verb with act  /ækt/ us  

(BECOME ACTIVE)

to become active: Her allergies acted up when she went hiking in the woods.
(Definition of act up phrasal verb, verb from the Cambridge Academic Content Dictionary © Cambridge University Press)
What is the pronunciation of act up?
Add Cambridge dictionaries to your browser to your website

Definitions of “act up” in other dictionaries

Word of the Day

hoppy

like hops (= dried fruit used to make beer)

Word of the Day

Blog

Read our blog about how the English language behaves.

Learn More

New Words

Find words and meanings that have just started to be used in English, and let us know what you think of them.

Learn More