mum's the word

Definition

Indicates that something is a secret and not to be divulged.

Etymology

From mum (“silence”). Recorded since 1704.

Example Sentences

• "She doesn't know anything about it yet, so mum's the word, OK?"
• "… and that mum is the word till I give you liberty to speak"
• "“Well, does she know how you feel?” “Honestly, Charmaine, I do not even know how I feel.” “Aw. Well, you should tell her.” “I should tell no one! Can you keep this secret, Charmaine?” “Mm-hmm.” “Good. Because if you don't, I'll kill you in your sleep.” “Okay, mum's the word.”"