Felis domesticus vs true cat

Felis domesticus and true cat both are nouns.

Word	Noun	Adjective	Verb	Adverb
Felis domesticus	Yes	No	No	No
true cat	Yes	No	No	No

As nouns, true cat is a hypernym of Felis domesticus; that is, true cat is a word with a broader meaning than Felis domesticus:

Felis domesticus: any domesticated member of the genus Felis
true cat: feline mammal usually having thick soft fur and no ability to roar: domestic cats; wildcats

Other hypernyms of Felis domesticus include domestic animal, domesticated animal, cat.

Felis domesticus (noun)	true cat (noun)
any domesticated member of the genus Felis	feline mammal usually having thick soft fur and no ability to roar: domestic cats; wildcats