From en.wikipedia.org:
[English idiom] [Other uses] MUM'S THE WORD is a popular English idiom. It is
related to an expression used by William Shakespeare, in _Henry VI, Part
2_.[1]
The word "mum" is an alteration of momme, which was used between 1350 and 1400
in Middle English with very close to the same meaning, "be silent; do not
reveal".
** Meaning
"Mum's the word" means to keep silent or quiet.
_Mum_ is a Middle English word meaning 'silent',[2] and may be derived from
the _mummer_ who acts without speaking.[3] Note the similar English word "mime
(see http://en.wiktionary.org/wiki/mime) " (Old English "mīma", Latin "mimus")
meaning silent actor or imitator.
** Origin
The origins of the phrase can be traced back to the fourteenth century and
William Langland's narrative poem, _Piers Plowman_:[Thou mightest beter meten
the myst on Malverne hulles <br/> Then geten a mom of heore mouth til moneye
weore schewed!]
It can also be seen in popular fifteenth-century Towneley Plays:[4][Though thi
lyppis be stokyn, yit myght thou say 'mum'.]
The phrase notably appears in Shakespeare's _Henry VI, Part 2_, Act 1, Scene
2:[Seal up your lips and give no words but mum.]
** References
[reflist]
[vocab-stub] [English-lang-stub]
Category:English-language idioms