Drink mate overturned (3)
I believe the answer is:
lap
'drink' is the definition.
(lap can mean to drink)
'mate overturned' is the wordplay.
'mate' becomes 'pal' (I've seen this before).
'overturned' shows that the letters should be reversed in order.
'pal' written backwards gives 'LAP'.
(Other definitions for lap that I've seen before include "Drink; lick" , "Use tongue to drink; circuit" , "Circuit (of a race track)" , "place for small computer?" , "One round of the course" .)