mum /mʌm/ Pronunciation Key - [muhm]
–adjective
1. silent; not saying a word: to keep mum.
–interjection
2. say nothing! be silent!
—Idiom
3. mum's the word, do not reveal what you know (about something); keep silent: Mum's the word, or the surprise party won't be a surprise.
"War doesn't determine who's right, just who's left" -Anonymous