Composer returning part for unmarried man (8)
I believe the answer is:
bachelor
'unmarried man' is the definition.
(synonyms)
'composer returning part' is the wordplay.
'composer' becomes 'bach' (Johann Sebastian Bach).
'returning' shows that the letters should be reversed in order.
'part' becomes 'role' (eg a theatrical role).
'role' back-to-front is 'elor'.
'bach'+'elor'='BACHELOR'
'for' acts as a link.
(Other definitions for bachelor that I've seen before include "Graduate" , "leading man at start of Wedding Cantata" , "he has no ties" , "Single man" , "Unmarried person" .)