Plum used to flavor spirits (4)
I believe the answer is:
sloe
'plum used to flavor spirits' is the definition.
(I've seen this in another clue)
This is all the clue.
(Other definitions for sloe that I've seen before include "Wild plum" , "Musical study" , "Fruit steeped in gin to make a liqueur" , "Sour blue-black fruit" , "Sour blackthorn fruit" .)