Keep a straight face
/kiːp ə streɪt feɪs/informalUK · US
What does “Keep a straight face” mean?
Keep a straight face means to avoid laughing or smiling when something is funny.
Keeping a straight face means hiding your amusement. You might be listening to a joke or trying to tell one without laughing.
It is light and conversational. Saying you could not keep a straight face usually invites the listener to share the joke.
When do people say it?
Use it when someone tries to look serious during a funny moment.
“I couldn’t keep a straight face when he tried on the hat.”
Is it formal or informal?
Register: informal. It is most at home in everyday conversation rather than formal writing. Most common in UK and US.
Where does it come from?
The image is of a face that stays serious rather than changing into a smile. The exact origin is not settled.
Origin confidence: Disputed; treat with caution
How do you say “Keep a straight face” in other languages?
Related idioms
- Pull someone's leg, To tease someone playfully.
- Play devil's advocate, Argue the opposite view to test an idea.
Last reviewed 2026-09-12