Drink knocked back after zero work (4)
I believe the answer is:
opus
'work' is the definition.
(I've seen this before)
'drink knocked back after zero' is the wordplay.
'drink' becomes 'sup' (I've seen this before**).
'knocked back' shows that the letters should be reversed in order.
'after' says to put letters next to each other.
'zero' becomes 'o'.
'sup' in reverse letter order is 'pus'.
'pus' after 'o' is 'OPUS'.
(Other definitions for opus that I've seen before include "Composer's work" , "Musical piece" , "Work of 25 perhaps" , "Composer's catalogue number" , "Work (mus.)" .)