Learn how to say Mum correctly in English with this tutorial pronunciation video.
Oxford dictionary definition of the word mum:
informal remain silent, especially so as not to reveal a secret:
he was keeping mum about a possible move to West Ham
mum’s the word
informal (as a request or warning) say nothing; do not reveal a secret:
I know I can rely upon your discretion, mum’s the word
late Middle English: imitative of a sound made with closed lips