River through Orsk (4)
I believe the answer is:
ural
'river through orsk' is the definition.
(I've seen this in another clue)
This is all the clue.
(Other definitions for ural that I've seen before include "Russian river, rising in the mountains between Europe and Asia" , "Asian flower" , "Russian river giving name to mountains" , "Runner" , "River feeding Caspian Sea" .)