Silent member of the family (3)
I believe the answer is:
mum
This clue is a double definition.
'silent' is the first definition.
(synonyms)
'member of the family' is the second definition.
(I've seen this before)
(Other definitions for mum that I've seen before include "Tight-lipped" , "Keep it secret from mother?" , "Parent (who's kept or is the word!)" , "Parent - shtoom" , "Silence" .)