A quiet father about to get large clothes (7)
I believe the answer is:
apparel
'clothes' is the definition.
(synonyms)
'a quiet father about to get large' is the wordplay.
'quiet' becomes 'p' (music symbol for 'piano', ie soft or quiet).
'father' becomes 'pa' (pa can mean dad or father).
'about to get' becomes 're' (I've seen this in other clues).
'large' becomes 'L' (eg in clothes sizes).
'a'+'p'+'pa'+'re'+'l'='APPAREL'
(Other definitions for apparel that I've seen before include "Formal word for clothing" , "Real pap (anag) - clothing" , "formal dress?" , "Raiment" , "Pod of peas" .)