Definition of mum's the word in English:

mum's the word

phrase

informal
  • (as a request or warning) say nothing; don't reveal a secret.

    ‘I know I can rely upon your discretion, mum's the word’
    • ‘For when it came to telling her mother of her dramatic ordeal, Jenny decided it was a case of mum's the word.’
    • ‘The mystery is certainly captivating Washington, while mum's the word at the White House.’
    • ‘But the best thing of all about all the hand-outs in this welfare state is that mum's the word, when it comes to explaining to taxpayers why you need their money.’
    • ‘He also said not to mention that I was paid to write an update for him, so mum's the word.’
    • ‘Go out and have some fun, but remember, mum's the word!’
    • ‘But she knew that it was going to be mum's the word and Faith would find out when she arrived in the principal's office Monday morning.’
    say nothing, keep quiet, don't breathe a word, don't tell a soul, don't give the game away, keep it secret, keep it to yourself, keep it under your hat, play dumb
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