Professor coming round with drink (4)
I believe the answer is:
down
'drink' is the definition.
(to down something can mean to drink it quickly)
'professor coming round with' is the wordplay.
'professor' becomes 'don' (term for a university professor).
'coming round' indicates putting letters inside.
'with' becomes 'w' (abbreviation).
'don' placed around 'w' is 'DOWN'.
(Other definitions for down that I've seen before include "Feathers or hair" , "In a low mood; hill" , "floor" , "like the other set of clues" , "Fuzz" .)