Nation on the Caspian (4)
I believe the answer is:
iran
'nation on the caspian' is the definition.
(I've seen this in another clue)
This is all the clue.
(Other definitions for iran that I've seen before include "Country lying to south of Caspian sea" , "Islamic republic on the Persian Gulf" , "Tehran's country" , "Previously known as Persia" , "Country to east of Iraq" .)