Bank security (4)
I believe the answer is:
lien
'bank security' is the definition.
(I've seen this in another clue)
This is the entire clue.
(Other definitions for lien that I've seen before include "Right to keep property" , "Right to another's property, if an obligation is not discharged" , "Right to a lawyer" , "Legal claim on the property of another" , "The right to take property if an obligation is not met" .)