Cambridge Dictionaries online Cambridge Dictionaries online

The most popular online dictionary and thesaurus for learners of English


English definition of “mum's the word”

mum's the word

saying old-fashioned
said when you tell someone, or agree with someone, to keep something a secret: "I'm not telling people generally yet." "OK, mum's the word!"Secrecy and privacy
(Definition of mum's the word from the Cambridge Advanced Learner's Dictionary & Thesaurus © Cambridge University Press)

Word of the Day


physical activity that you do to make your body strong and healthy

Word of the Day


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