Ring a fellow in sultanate (4)
I believe the answer is:
oman
'sultanate' is the definition.
(Sultanate of Oman, Middle Eastern country)
'ring a fellow' is the wordplay.
'ring' becomes 'O' (O is the shape of a ring).
'a fellow' becomes 'man' (fellow can mean a man).
'o'+'man'='OMAN'
'in' acts as a link.
(Other definitions for oman that I've seen before include "Arabian country, capital Muscat" , "Middle Eastern country" , "monarchy" , "Former Gulf country, Muscat and --" , "Sultanate on the south-east coast of the Arabian Peninsula" .)