Cask sediment (4)
I believe the answer is:
lees
'cask sediment' is the definition.
(I've seen this in another clue)
This is all the clue.
(Other definitions for lees that I've seen before include "Sediment that settles at the bottom of liquid" , "Dregs, sediment" , "Sediment that settles at the bottom of wine" , "Deposit" , "Knock back these dregs of liquor" .)