Cách sử dụng
The expression "mum's the word" is used when someone wants to tell you a secret and wants you to keep it a secret too. It means you should not tell anyone else what you have been told. It is like promising to keep your mouth shut and not share the secret with anyone. For example, if someone tells you about a surprise party for a friend, they might say "mum's the word" so you know not to tell the friend and spoil the surprise.