Justification for a deposit (7)
I believe the answer is:
grounds
I believe this clue is a double definition.
'justification for' is the first definition.
(I've seen this before)
'a deposit' is the second definition.
(grounds is a kind of deposit)
(Other definitions for grounds that I've seen before include "Basis for belief" , "they make coffee" , "Reasons" , "reason" , "Area of enclosed land around a building" .)