tortoiseshell vs Felis catus

tortoiseshell and Felis catus both are nouns.

Word	Noun	Adjective	Verb	Adverb
tortoiseshell	Yes	No	No	No
Felis catus	Yes	No	No	No

As nouns, Felis catus is a hypernym of tortoiseshell; that is, Felis catus is a word with a broader meaning than tortoiseshell:

Other hypernyms of tortoiseshell include domestic cat, Felis domesticus, house cat.

tortoiseshell (noun)	Felis catus (noun)
a cat having black and cream-colored and yellowish markings	any domesticated member of the genus Felis
brilliantly colored; larvae feed on nettles
the mottled horny substance of the shell of some turtles