The region encompassing Arabian Sea (4)
I believe the answer is:
Here is my best explanation:
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 don't understand how one could define the other.
(Other definitions for area that I've seen before include "Length multiplied by breadth", "Region, space", "Locality", "Part of a building, city etc", "Region, zone", "District; locale", "Speaking formally to (someone)", "A zone", "Field of activity or surface" and "land".)