River over in Belarus (4)
I believe the answer is:
ural
'river' is the definition.
(I've seen this in other clues)
'over in belarus' is the wordplay.
'over' is a reversal indicator.
'in' indicates a hidden word.
'laru' is hidden in the letters of 'belarus'.
'laru' back-to-front is 'URAL'.
(Other definitions for ural that I've seen before include "2,400 km river flowing through Russia and Kazakhstan into the Caspian Sea" , "Runner" , "Mountains in Russia" , "Europe/Asia river" , "Russian river giving name to mountain range" .)