Arab state in Ottoman Empire (4)
I believe the answer is:
oman
'arab state' is the definition.
(Oman is a Middle Eastern country)
'in ottoman empire' is the wordplay.
'in' indicates a hidden word.
'OMAN' is hidden in the letters of 'ottoman empire'.
(Other definitions for oman that I've seen before include "Arab state" , "Middle Eastern country" , "Sultanate in southwest Asia" , "Gulf sultanate" , "Former Gulf country, Muscat and --" .)