'mum's the word' definitions:

Definition of 'mum's the word'

From: GCIDE
  • Mum \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. --Shak. [1913 Webster]
  • mum's the word keep this a secret; don't tell anybody. [PJC]