Not much of a drink (3)
I believe the answer is:
sip
'a drink' is the definition.
(I've seen this in another clue)
I don't understand how the remainder of the clue works.
Can you help me to learn more?
(Other definitions for sip that I've seen before include "Small mouthful of fluid" , "Take small mouthfuls of (drink)" , "Thimbleful" , "A small taste" , "Small mouthful of liquid" .)