Pre-dinner drink (8)
I believe the answer is:
'pre-dinner drink' is the definition.
(I've seen this before)
This is the entire clue.
(Other definitions for aperitif that I've seen before include "Pre-nosh tipple?" , "Preprandial tipple" , "Alcoholic drink to stimulate appetite" , "alcohol before meal" , "An alcoholic drink before dinner, an appetiser" .)