mum’s the word
Meaning
Keep it secret; don’t tell anyone.
Origin
Recorded from the early 18th century. “Mum” is an old word meaning “silent” or “not speaking” (like making the sound “mm”), so the phrase signals that silence is required.
Notes
Means “keep quiet/keep it confidential.” Often said when sharing a secret; slightly old-fashioned but still understood.
Examples
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Don’t worry—I won’t mention it to anyone; mum’s the word.
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We’re throwing her a surprise party, so mum’s the word until Saturday.
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He asked me to keep the new product launch quiet, and I agreed: mum’s the word.
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If the boss asks about the job search, mum’s the word, okay?
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The kids promised that mum’s the word about the hidden presents in the closet.
Grammar & Usage Notes
Fixed phrase; usually used as a standalone statement (“Mum’s the word.”). Also appears after a condition (“Mum’s the word, okay?”). Often written with an apostrophe (mum’s), sometimes as “mum’s the word” or “mum’s the word!”
Synonyms
- keep it under your hat
- keep it to yourself
- keep it quiet
- keep it secret
- don’t breathe a word
Antonyms
- spill the beans
- let the cat out of the bag