Prospero's playing the tyrant (9)
I believe the answer is:
oppressor
'the tyrant' is the definition.
(I've seen this before)
'prospero's playing' is the wordplay.
'playing' is an anagram indicator.
'prosperos' with letters rearranged gives 'OPPRESSOR'.
(Other definitions for oppressor that I've seen before include "Persecutor of proposers" , "One tyrannises" , "Tyrant" , "One who keeps another in subjection" , "One subjects others to undue pressure" .)