Cask dregs
I believe the answer is:
lees
'cask dregs' 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 "worst part" , "Sediment that settles at the bottom of liquid" , "Eels found in sediment" , "Sediment from fermentation of alcohol" , "Wine dregs" .)