tundra vs champaign

tundra and champaign both are nouns.

Word	Noun	Adjective	Verb	Adverb
tundra	Yes	No	No	No
champaign	Yes	No	No	No

As nouns, champaign is a hypernym of tundra; that is, champaign is a word with a broader meaning than tundra:

tundra: a vast treeless plain in the Arctic regions where the subsoil is permanently frozen
champaign: extensive tract of level open land

Other hypernyms of tundra include field, plain.

tundra (noun)	champaign (noun)
a vast treeless plain in the Arctic regions where the subsoil is permanently frozen	extensive tract of level open land