Extremely cold drink (6)
I believe the answer is:
bitter
I believe this clue is a double definition.
'extremely cold' is the first definition.
(bitterly cold)
'drink' is the second definition.
(bitter is a kind of drink)
(Other definitions for bitter that I've seen before include "Acrid - beer" , "Sour tasting, like English ale" , "severe" , "Tart like some English beer" , "Sharp-tasting or resentful" .)