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