mum

• POS: Adjective, Noun, Verb (usu participle)

CIDE DICTIONARY

mum, a. [Of imitative origin. Cf. Mumble.].

 Silent; not speaking; as, to keep mum.  Thackeray.  [1913 Webster]
"The citizens are mum, and speak not a word."  [1913 Webster]

mum's the word keep this a secret; don't tell anybody.

mum, interj. 

 Be silent! Hush!  [1913 Webster]
"Mum, then, and no more."  [1913 Webster]

mum, n. 

 Silence.  Hudibras.  [1913 Webster]

mum, n. [G. mummere, fr. Christian Mumme, who first brewed it in 1492.].

 A sort of strong beer, originally made in Brunswick, Germany.  Addison.  [1913 Webster]
"The clamorous crowd is hushed with mugs of mum."  [1913 Webster]

OXFORD DICTIONARY

mum, n. Brit. colloq. mother.

mum, adj. colloq. silent (keep mum).

Idiom

mum's the word say nothing.

mum, v.intr. (mummed, mumming) act in a traditional masked mime.

Etymology

cf. MUM(2) and MLG mummen

THESAURUS

mum

anaudic, aphasic, aphonic, breathless, brief, brusque, close, close-tongued, closemouthed, concise, curt, dumb, dumbfounded, dumbstricken, dumbstruck, economical of words, inarticulate, indisposed to talk, laconic, ma, mam, mama, mammy, mater, mom, mommy, mummy, mute, old woman, quiet, short, silent, snug, sparing of words, speechless, stricken dumb, taciturn, terse, tight-lipped, tongue-tied, tongueless, unloquacious, untalkative, voiceless, word-bound, wordless

ROGET THESAURUS

mum

Aphony

N aphony, aphonia, dumbness, obmutescence, absence of voice, want of voice, dysphony, cacoepy, silence, raucity, harsh voice &c, unmusical voice, falsetto, childish treble mute, dummy, aphonous, dumb, mute, deafmute, deaf and dumb, mum, tongue-tied, breathless, tongueless, voiceless, speechless, wordless, mute as a fish, mute as a stockfish, mute as a mackerel, silent, muzzled, inarticulate, inaudible, croaking, raucous, hoarse, husky, dry, hollow, sepulchral, hoarse as a raven, rough, with bated breath, with the finger on the lips, sotto voce, in a low tone, in a cracked voice, in a broken voice, vox faucibus haesit.

Taciturnity

N taciturnity, silence, muteness, obmutescence, taciturnity, pauciloquy, costiveness, curtness, reserve, reticence, man of few words, silent, mute, mum, silent as a post, silent as a stone, silent as the grave, dumb, unconversable, taciturn, sparing of words, closetongued, costive, inconversable, curt, reserved, reticent, Int, shush!, tush!, silence!, mum!, hush!, chut!, hist!, tut!, chup!, mum's the word, keep your mouth shut!, cave quid dicis quando et cui, volto sciolto i pensieri stretti.