A Greek wine (7)
I believe the answer is:
retsina
'a greek wine' is the definition.
(I've seen this before)
This is all the clue.
(Other definitions for retsina that I've seen before include "Flavoured Greek white wine - nastier brand" , "Nastier (anag) - white (or rose) wine" , "Greek wine - nastier sort" , "Greek resin-flavoured wine" , "Nastier (anag) - Greek wine" .)