Glug (4)
I believe the answer is:
swig
'glug' is the definition.
(I've seen this in another clue)
This is the entire clue.
(Other definitions for swig that I've seen before include "Drink in large draughts" , "Drink quickly from bottle" , "Glug" , "Drink (a deep draught)" , "Large draught of drink" .)