Drunk Greek character returned before (5)
I believe the answer is:
until
'before' is the definition.
(thesaurus)
'drunk greek character returned' is the wordplay.
'drunk' becomes 'lit' (I've seen this in other clues**).
'greek character' becomes 'nu' (letter from the Greek alphabet).
'returned' says the letters should be written in reverse.
'lit'+'nu'='litnu'
'litnu' back-to-front is 'UNTIL'.
(Other definitions for until that I've seen before include "Pending such time as" , "Not beyond (hour)" , "Before a given time" , "Unlit (anag.)" , "Up to (a point in time)" .)