Mother; silent (3)
I believe the answer is:
mum
I believe this is a double definition.
'mother' is the first definition.
(informal term for mother)
'silent' is the second definition.
(synonyms)
(Other definitions for mum that I've seen before include "Mother - she's the word for secrecy" , "Parent (who's kept or is the word!)" , "Mother (colloq.)" , "old lady" , "Parent - shtoom" .)