Sultanate in Borneo (6)
I believe the answer is:
brunei
'sultanate in borneo' is the definition.
(I've seen this in another clue)
This is all the clue.
(Other definitions for brunei that I've seen before include "Ill" , "Muslim state" , "Sultanate of southeast Asia" , "Sultanate in northwest Borneo" , "Its sultan is famously very wealthy" .)