Single chap, barman, withdrawn character (8)
I believe the answer is:
bachelor
'single chap' is the definition.
(an unmarried man)
'barman withdrawn character' is the wordplay.
'barman' becomes 'bach' (Bach, a composer responsible for bars of music).
'withdrawn' shows that the letters should be reversed in order.
'character' becomes 'role' (synonyms).
'role' back-to-front is 'elor'.
'bach'+'elor'='BACHELOR'
(Other definitions for bachelor that I've seen before include "Graduate" , "Unmarried person" , "Non-married male" , "He's not married" , "Unmarried male" .)