Castor vs mammal genus

Castor and mammal genus both are nouns.

Word	Noun	Adjective	Verb	Adverb
Castor	Yes	No	No	No
mammal genus	Yes	No	No	No

As nouns, mammal genus is a hypernym of Castor; that is, mammal genus is a word with a broader meaning than Castor:

Castor (noun)	mammal genus (noun)
type genus of the Castoridae: beavers	a genus of mammals
a multiple star with 6 components; second brightest in Gemini; close to Pollux