Seize wrongfully (5)
I believe the answer is:
usurp
'seize wrongfully' is the definition.
(I've seen this before)
This is all the clue.
(Other definitions for usurp that I've seen before include "Take (power) by force or illegally" , "Take (power etc) illegally" , "Seize without right" , "Take over - misappropriate" , "Seize, take over" .)