Possibly retains a Greek drink (7)
I believe the answer is:
retsina
'a greek drink' is the definition.
(I've seen this before)
'possibly retains' is the wordplay.
'possibly' is an anagram indicator.
'retains' is an anagram of 'RETSINA'.
(Other definitions for retsina that I've seen before include "Oily-tasting Greek white wine" , "S European wine" , "Greek drink" , "Greek wine - nastier sort" , "Nastier (anag) - Greek wine" .)