act up Informal

Meaning: If a part of your body or a piece of equipment acts up, it doesn't work properly.

Synonym: play up, malfunction

For example:

act up My printer is acting up, so I'll have to get it fixed.
act up I'll have to give the tennis a miss this week. My knee is acting up again.

Nouns often used as subjects with
act up: computer, printer, phone, air conditioner, knee, wrist, ankle, stomach

Quick Quiz:

If your computer's acting up, it's

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