Russian plain (6)
I believe the answer is:
steppe
'russian plain' is the definition.
(I've seen this in another clue)
This is the entire clue.
(Other definitions for steppe that I've seen before include "Large treeless area of Siberia" , "Dry area of grassland in southeast Europe and Siberia" , "Large area of unforested grassland" , "Large area of flat grassland in Europe or Siberia" , "Dry plain of Eurasia" .)