One of two sultanates in the United Nations
(Other definitions for brunei that I've seen before include "Southeast Asian sultanate" , "Sultanate on the island of Borneo" , "Commonwealth country" , "Oil-rich country of Southeast Asia" , "Its sultan is famously very wealthy" .)
(Other definitions for oman that I've seen before include "Sultanate on the south-east coast of the Arabian Peninsula" , "Arabian country, capital Muscat" , "Former Gulf country, Muscat and --" , "Arab state" , "Arab country" .)