Renounce one’s throne (8)
I believe the answer is:
abdicate
'renounce one's throne' is the definition.
(I've seen this before)
This is all the clue.
(Other definitions for abdicate that I've seen before include "Renounce position or power" , "Give up a throne" , "Resign from the crown or major responsibility" , "Resign from or renounce the throne" , "Give up rule" .)