Willing mage to get drunk (4)
I believe the answer is:
game
'willing' is the definition.
(thesaurus)
'mage to get drunk' is the wordplay.
'to get drunk' is an anagram indicator.
'mage' is an anagram of 'GAME'.
(Other definitions for game that I've seen before include "Scrabble or Monopoly, say" , "Birds hunted for food" , "Hunted animals or birds" , "venison, say" , "Prepared" .)