Greek characters leaving French wine for trainee (5)
I believe the answer is:
cadet
'for trainee' is the definition.
(cadet is a kind of trainee)
'greek characters leaving french wine' is the wordplay.
'greek characters' becomes 'mus' (more than one mu - mu is a Greek letter).
'leaving' suggests deleting specific letters.
'french wine' becomes 'muscadet'.
'muscadet' with 'mus' removed is 'CADET'.
(Other definitions for cadet that I've seen before include "junior role" , "Trainee soldier" , "Potential officer" , "not the heir" , "Younger son" .)