Mum /(?)/

Mum

a.
  1. Silent; not speaking; as, to keep mum.
    The citizens are mum, and speak not a word.

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

Mum

interj.
  1. Be silent! Hush!
    Mum, then, and no more.

Mum

n.
  1. Silence. [R.]

Mum

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 A sort of strong beer, originally made in Brunswick, Germany.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