The region encompassing Arabian Sea (4)
I believe the answer is:
area
This clue might be a double definition.
'the region' is the first definition.
(area is a kind of region)
'encompassing arabian sea' is the second definition.
Although both the answer and definition are singular nouns, I can't see how one could define the other.
Can you help me to learn more?
(Other definitions for area that I've seen before include "Length multiplied by breadth" , "Expanse or neighbourhood" , "Space for a specific purpose, say picnic" , "Territory" , "Region; extent of a surface" .)