gerbil vs gnawer

gerbil and gnawer both are nouns.

Word	Noun	Adjective	Verb	Adverb
gerbil	Yes	No	No	No
gnawer	Yes	No	No	No

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

gerbil: small Old World burrowing desert rodent with long soft pale fur and hind legs adapted for leaping
gnawer: relatively small placental mammals having a single pair of constantly growing incisor teeth specialized for gnawing

Other hypernyms of gerbil include rodent.

gerbil (noun)	gnawer (noun)
small Old World burrowing desert rodent with long soft pale fur and hind legs adapted for leaping	relatively small placental mammals having a single pair of constantly growing incisor teeth specialized for gnawing