Had a debt (4)
I believe the answer is:
owed
'had a debt' is the definition.
('owe' can be a synonym of 'have a debt')
This is all the clue.
(Other definitions for owed that I've seen before include "Was obliged to pay" , "Was indebted" , "to be paid" , "Was due to pay" , "Had an obligation to pay" .)