African expression of disapproval one's rebuffed (5)
I believe the answer is:
tutsi
'african' is the definition.
(the Tutsi are an African ethnic group)
'expression of disapproval one's rebuffed' is the wordplay.
'expression of disapproval' becomes 'tut' (sound made to express disapproval).
'one's' becomes 'i's' (Roman numeral).
'rebuffed' shows that the letters should be reversed in order.
'is' reversed gives 'si'.
'tut'+'si'='TUTSI'
(Other definitions for tutsi that I've seen before include "Person from Burundi" , "Rwandan group" , "Tribespeople" , "Member of a Bantu people of Rwanda and Burundi" , "Ethnic group of Rwanda and Burundi" .)