Idiom
Mum's the word
Mum's the word means "say nothing": it is a promise, or a request, to keep something secret.
How people use it
People say it to agree to keep a secret ("Don't worry, mum's the word") or to ask someone else to stay quiet ("The party is a surprise, so mum's the word"). It is friendly and informal, and it is most often used for happy secrets like gifts and surprises. The related phrase "keep mum" means stay silent. The word here has nothing to do with mothers, even though British English spells its word for "mom" the same way.
Also said: keep mum.
Examples
- We're planning a surprise party for Dad, so mum's the word.
- When Priya told me about her new job offer, I promised her mum's the word.
- The kids know where the presents are hidden, but mum's the word until the holidays.
Where it comes from
This "mum" imitates the sound you make with your lips pressed shut, a closed-mouth "mmm." English has used it to mean silence since the Middle Ages. Shakespeare used it in Henry VI, Part 2, where a character says to "give no words but mum." The exact phrase "mum's the word" is recorded by the 1700s.
Check yourself
1. Your friend tells you about a surprise and adds, "Mum's the word." What should you do?
Answer: Keep it secret. The phrase asks you to stay quiet and keep the secret.
2. Where does the first word of this idiom come from?
Answer: The sound of closed lips. It imitates the sound made with the mouth shut, so it stands for silence.
Similar idioms
Word game fan? See every word hiding in MUM.