jaguar vs big cat

jaguar and big cat both are nouns.

Word	Noun	Adjective	Verb	Adverb
jaguar	Yes	No	No	No
big cat	Yes	No	No	No

As nouns, big cat is a hypernym of jaguar; that is, big cat is a word with a broader meaning than jaguar:

jaguar: a large spotted feline of tropical America similar to the leopard; in some classifications considered a member of the genus Felis
big cat: any of several large cats typically able to roar and living in the wild

Other hypernyms of jaguar include cat.

jaguar (noun)	big cat (noun)
a large spotted feline of tropical America similar to the leopard; in some classifications considered a member of the genus Felis	any of several large cats typically able to roar and living in the wild