Alcoholic drink involves a big belly (6)
I believe the answer is:
paunch
'big belly' is the definition.
(a paunch is a large belly)
'alcoholic drink involves a' is the wordplay.
'alcoholic drink' becomes 'punch'.
'involves' is an insertion indicator.
'punch' enclosing 'a' is 'PAUNCH'.
(Other definitions for paunch that I've seen before include "Protuberant stomach" , "Large stomach or belly" , "Protruding belly" , "Protuberant belly" , "Pot" .)