Single drink (3)
I believe the answer is:
one
I believe this clue is a double definition.
'single' is the first definition.
(synonyms)
'drink' is the second definition.
(eg 'a cold one')
(Other definitions for one that I've seen before include "SECOND PART OF 16" , "Identical; number" , "Unity" , "Half of two" , "A certain; single person" .)