Mum
WordNet
adjective
(1) Failing to speak or communicate etc when expected to
"The witness remained silent"
noun
(2) Secrecy
"Mum's the word"
(3) Informal terms for a mother
(4) Of China
WiktionaryText
Usage notes
Mum is only capitalized when used as a proper noun:
- I don't think Mum will like you.
- I don't think my mum will like you.