A quiet Mum or Dad is evident (8)
I believe the answer is:
apparent
'evident' is the definition.
(synonyms)
'a quiet mum or dad' is the wordplay.
'a quiet' becomes 'ap' (I've seen this in other clues).
'mum or dad' becomes 'parent' (I've seen this before).
'ap'+'parent'='APPARENT'
'is' acts as a link.
(Other definitions for apparent that I've seen before include "Obvious; seemingly true" , "Evident, manifest" , "That may be seen" , "Seeming to be but not necessarily so" , "Obvious, evident" .)