Siamese cat vs Felis domesticus

Siamese cat and Felis domesticus both are nouns.

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

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

Siamese cat: a slender short-haired blue-eyed breed of cat having a pale coat with dark ears paws face and tail tip
Felis domesticus: any domesticated member of the genus Felis

Other hypernyms of Siamese cat include domestic cat, Felis catus, house cat.

Siamese cat (noun)	Felis domesticus (noun)
a slender short-haired blue-eyed breed of cat having a pale coat with dark ears paws face and tail tip	any domesticated member of the genus Felis