River of Russia (4)
I believe the answer is:
ural
<span class="explanation-format__ClueExplanation">'<span class="explanation-format__original">river of russia</span>' is the definition.<br/ ><span class="explanation-format__explanation">(I've seen this before)</span><br/ ><br/ >This is all the clue.<br/ ></span>
(Other definitions for ural that I've seen before include "The - mountains separate Asia and Europe" , "Russian river flowing into the Caspian Sea" , "Mountain range between Europe and Asia" , "Europe/Asia river" , "2,400 km river flowing through Russia and Kazakhstan into the Caspian Sea" .)