Ace partner sure peeled in buff (7)
I believe the answer is:
amateur
'buff' is the definition.
(thesaurus)
'ace partner sure peeled' is the wordplay.
'ace' becomes 'a' (abbreviation).
'partner' becomes 'mate' (synonyms).
'peeled' means to look at the middle letters (outer letters are peeled off).
The middle of 'sure' is 'ur'.
'a'+'mate'+'ur'='AMATEUR'
'in' acts as a link.
(Other definitions for amateur that I've seen before include "Unpaid performer" , "Non-pro" , "Unpaid (sports)" , "Unpaid player" , "Unpaid practitioner" .)