Despotism (7)
I believe the answer is:
tyranny
'despotism' is the definition.
(I know that despotism can be written as tyranny)
This is all the clue.
(Other definitions for tyranny that I've seen before include "Reign of terror" , "Cruel rulers" , "Excessive use of power" , "Despotic rule" , "Oppressive government" .)