Matey missing quiet colleague (4)
I believe the answer is:
ally
'colleague' is the definition.
(I've seen this before)
'matey missing quiet' is the wordplay.
'matey' becomes 'pally' ('pally' can be a synonym of 'matey').
'missing' is a deletion indicator.
'quiet' becomes 'p' (music symbol for 'piano').
'pally' with 'p' taken out is 'ALLY'.
(Other definitions for ally that I've seen before include "Comrade in arms" , "Accomplice" , "Collaborator, affiliate" , "Join by marriage, treaty etc" , "A friendly and reliable country" .)