leopard vs panther

leopard and panther both are nouns.

Word	Noun	Adjective	Verb	Adverb
leopard	Yes	No	No	No
panther	Yes	No	No	No

As nouns, panther is a hyponym of leopard; that is, panther is a word with a more specific, narrower meaning than leopard:

leopard: large feline of African and Asian forests usually having a tawny coat with black spots
panther: a leopard in the black color phase

Other hyponyms of leopard include leopardess.

leopard (noun)	panther (noun)
large feline of African and Asian forests usually having a tawny coat with black spots	a leopard in the black color phase
the pelt of a leopard	a large spotted feline of tropical America similar to the leopard; in some classifications considered a member of the genus Felis
	large American feline resembling a lion