Be in arrears (3)
I believe the answer is:
owe
'be in arrears' is the definition.
(I've seen this in another clue)
This is all the clue.
(Other definitions for owe that I've seen before include "Are debtors" , "Be obliged to pay" , "Have outstanding" , "have favours to return" , "Be in debt - woe is me" .)