Swallow most of drink (6)
I believe the answer is:
martin
'swallow' is the definition.
(martin is a kind of swallow)
'most of drink' is the wordplay.
'most of' means to remove the last letter.
'drink' becomes 'martini' (martini is a kind of drink).
'martini' with its last letter removed is 'MARTIN'.
(Other definitions for martin that I've seen before include "Tweeter" , "Small swallow" , "Creature that flies" , "Swallow-like bird" , "Bird; in tram (anag.)" .)