mountain beaver vs gnawer

mountain beaver and gnawer both are nouns.

Word	Noun	Adjective	Verb	Adverb
mountain beaver	Yes	No	No	No
gnawer	Yes	No	No	No

As nouns, gnawer is a hypernym of mountain beaver; that is, gnawer is a word with a broader meaning than mountain beaver:

mountain beaver: bulky nocturnal burrowing rodent of uplands of the Pacific coast of North America; the most primitive living rodent
gnawer: relatively small placental mammals having a single pair of constantly growing incisor teeth specialized for gnawing

Other hypernyms of mountain beaver include rodent.

mountain beaver (noun)	gnawer (noun)
bulky nocturnal burrowing rodent of uplands of the Pacific coast of North America; the most primitive living rodent	relatively small placental mammals having a single pair of constantly growing incisor teeth specialized for gnawing