Ancient Middle East kingdom, way back (4)
I believe the answer is:
edom
'ancient middle east kingdom' is the definition.
(ancient Arab kingdom)
'way back' is the wordplay.
'way' becomes 'mode' (synonyms).
'back' shows that the letters should be reversed in order.
'mode' in reverse letter order is 'EDOM'.
(Other definitions for edom that I've seen before include "Kingdom of the Middle East" , "Ancient people" , "Biblical land" , "Backward manner of existence" , "In the Bible, the land of the people of Esau" .)