mum's the word
Proposed by a contributor, not yet supported by evidence.
Meaning · English
Recognized English idiom; full definition pending editorial review.
Where it’s used:
Used
Widespread English
Examples
‘ I know I can rely upon your discretion, mum's the word,’ his constituency chairman continued, ‘ but all the publicity she has been getting has gone to her head.
So mum's the word, all right?’
British National Corpus sentence via the MAGPIE corpus (CC BY 4.0, retrieved 2026-07-30)
Sources & notes
Listed in Wiktionary’s “English idioms” category (retrieved 2026-07-29); definition pending editorial review.
Common questions
What does “mum's the word” mean?
Recognized English idiom; full definition pending editorial review.
Is “mum's the word” formal or informal?
No register label has been reviewed yet — treat it as neutral and check the usage notes above.