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mum

Someone who's mum has nothing to say, especially on a particular subject. If you agree to keep someone's secret, you could tell them, "Mum's the word!"

A shy child who's new at school might stay mum all day, and even your most talkative friend might remain mum on controversial topics like religion and politics. In many parts of the world, mum is also a nickname for your mother — and it's also a nickname for the flower called a chrysanthemum. The "quiet" meaning of mum comes from Old English, inspired by the "mmm" sound you make when your lips are closed.

Definitions of mum
  1. adjective
    failing to speak or communicate etc when expected to
    synonyms: silent
    incommunicative, uncommunicative
    not inclined to talk or give information or express opinions
  2. noun
    secrecy
    mum's the word”
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    type of:
    secrecy, secretiveness, silence
    the trait of keeping things secret
  3. noun
    informal terms for a mother
    synonyms: ma, mama, mamma, mammy, mom, momma, mommy, mummy
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    type of:
    female parent, mother
    a woman who has given birth to a child (also used as a term of address to your mother)
  4. noun
    of China
    synonyms: Chrysanthemum morifolium, Dendranthema grandifloruom, florist's chrysanthemum, florists' chrysanthemum
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    type of:
    chrysanthemum
    any of numerous perennial Old World herbs having showy brightly colored flower heads of the genera Chrysanthemum, Argyranthemum, Dendranthema, Tanacetum; widely cultivated
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