Panthera tigris vs big cat

Panthera tigris and big cat both are nouns.

Word	Noun	Adjective	Verb	Adverb
Panthera tigris	Yes	No	No	No
big cat	Yes	No	No	No

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

Panthera tigris: large feline of forests in most of Asia having a tawny coat with black stripes; endangered
big cat: any of several large cats typically able to roar and living in the wild

Other hypernyms of Panthera tigris include cat.

Panthera tigris (noun)	big cat (noun)
large feline of forests in most of Asia having a tawny coat with black stripes; endangered	any of several large cats typically able to roar and living in the wild