Quiet man's friend (3)
I believe the answer is:
pal
'friend' is the definition.
(pal can mean a friend)
'quiet man's' is the wordplay.
'quiet' becomes 'p' (music symbol for 'piano', ie soft or quiet).
'man' becomes 'al' (man's name).
'p'+'al'='PAL'
(Other definitions for pal that I've seen before include "Buddy, chum" , "Brother" , "Bud" , "Friend (colloq.)" , "Crony" .)