gerbil vs rodent

gerbil and rodent both are nouns.

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

As nouns, rodent is a hypernym of gerbil; that is, rodent 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
rodent: relatively small placental mammals having a single pair of constantly growing incisor teeth specialized for gnawing

Other hypernyms of gerbil include gnawer.

gerbil (noun)	rodent (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