Webster's Revised Unabridged Dictionary · 1913

Mum

Mum , adjective

[Of imitative origin. Compare Mumble.]

Silent; not speaking; as, to keep mum. — Thackeray
The citizens are mum, and speak not a word. — Shakespeare
Collocations (1)
mum's the word , keep this a secret; don't tell anybody.

Mum , interjection

Be silent! Hush!
Mum, then, and no more. — Shakespeare

Mum , noun

Silence. [Rare] — Hudibras

Mum , noun

[German mummere, from Christian Mumme, who first brewed it in 1492.]

A sort of strong beer, originally made in Brunswick, Germany. — Addison
The clamorous crowd is hushed with mugs of mum. — Pope