Arabian sultanate (4)
I believe the answer is:
oman
<span class="explanation-format__ClueExplanation">'<span class="explanation-format__original">arabian sultanate</span>' is the definition.<br/ ><span class="explanation-format__explanation">(Oman is ruled by a sultan)</span><br/ ><br/ >This is the entire clue.<br/ ></span>
(Other definitions for oman that I've seen before include "Sultanate on the south-east coast of the Arabian Peninsula" , "Arab country" , "Gulf state" , "Gulf sultanate" , "Arab state" .)