Head of state’s power over inhabitant (9)
I believe the answer is:
president
'head of state's' is the definition.
(president is a type of head of state)
'power over inhabitant' is the wordplay.
'power over' becomes 'p' (I've seen this in other clues).
'inhabitant' becomes 'resident' (resident is a kind of inhabitant).
'p'+'resident'='PRESIDENT'
(Other definitions for president that I've seen before include "Head of state has an odd red instep" , "Wilson once" , "club official" , "Grant perhaps" , "2's official title" .)