Dexter's prerogative? (5)
I believe the answer is:
right
I believe this clue is a double definition.
'dexter's' is the first definition.
(thesaurus)
'prerogative?' is the second definition.
(prerogative is a kind of right)
(Other definitions for right that I've seen before include "True - just claim" , "OK?" , "Morally good, justifiable or acceptable" , "Fit" , "blue, politically" .)