mum's the word
Indicates that something is a secret and not to be divulged.
Meaning adapted from Wiktionary, available under CC BY-SA 4.0.
“I have a surprise for him, so mum's the word.”
“I am leaving my job soon, but mum's the word for now.”
“If you find the hidden cookies, remember that mum's the word.”
“We are planning a surprise party for our boss, but remember that mum's the word until Friday.”
“I know you saw who broke the window, but mum's the word because I do not want to get our friend in trouble.”
“The doctor told me the baby's gender today, and since my husband wants a surprise, mum's the word during dinner.”
“We found a cheaper way to fix the car, but mum's the word so the mechanic does not raise his prices next time.”
“She whispered the details of the confidential merger to her partner, adding that mum's the word until the official announcement is made to the press.”
first recorded 18th c.
First recorded in 1704, the expression is derived from the Middle English *mum*, a representation of the sound made with a closed mouth to signal silence. The term functioned as a directive to remain quiet long before the full phrase became a standard idiom.
- 01
bad word
A vulgar word.
- 02
breathe a word
To divulge even part of a secret (usually used with a negative).
- 03
dicky
[Cockney slang]word
- 04
dirty word
The name of a topic that a person prefers not to hear or discuss.
- 05
empty words
Any type of talk with little meaning; a message that seems to contain meaningful content but is actually vapid.
- 06
from the word go
From the very beginning; from the outset; immediately upon starting.
- 07
get the word out
To make some information more widely known.
- 08
hang on every word
To be completely attentive to what another person is saying.
Last updated August 10, 2026