Debt: remove lid from jar (4)
I believe the answer is:
hock
'debt' is the definition.
(I've seen this in another clue)
'remove lid from jar' is the wordplay.
'remove lid from' means to remove the first letter (in a down clue, the lid is the top letter).
'jar' becomes 'shock' (I've seen this before).
'shock' with its initial letter taken off is 'HOCK'.
(Other definitions for hock that I've seen before include "Buy property, say" , "German wine -- horse's back 'ankle'" , "Uncle's pledge" , "Dry wine; joint; pawn" , "Dry Rhine wine" .)