Gaucho's plain (5)
I believe the answer is:
llano
'gaucho's plain' is the definition.
(I've seen this in another clue)
This is the entire clue.
(Other definitions for llano that I've seen before include "Treeless grassy plain in South America" , "Treeless area" , "(South American) grassy plain" , "Grassy plain in South?America" , "Flat area" .)