Some monument undraped and plain (6)
I believe the answer is:
tundra
'plain' is the definition.
(tundra is a kind of plain)
'some monument undraped and' is the wordplay.
'some' says the answer is hidden in the clue (some of the parts of the word are used).
'TUNDRA' can be found hidden inside 'monument undraped and'.
(Other definitions for tundra that I've seen before include "Arctic plain with permanently frozen subsoil" , "Vast level Arctic region with frozen subsoil" , "wasteland" , "Vast flat treeless zone" , "Treeless frozen Arctic plain" .)