River to the Caspian (4)
I believe the answer is:
ural
'river to the caspian' is the definition.
(I've seen this in another clue)
This is the entire clue.
(Other definitions for ural that I've seen before include "Europe/Asia river" , "Russian river giving name to mountain range" , "2,400 km river flowing through Russia and Kazakhstan into the Caspian Sea" , "Asian flower" , "Mountain range between Europe and Asia" .)