panther vs mountain lion

panther and mountain lion both are nouns.

Word	Noun	Adjective	Verb	Adverb
panther	Yes	No	No	No
mountain lion	Yes	No	No	No

As nouns, panther and mountain lion are synonyms defined as:

Other synonyms of panther include catamount, cougar, Felis concolor, painter, puma.

panther (noun)	mountain lion (noun)
a leopard in the black color phase	large American feline resembling a lion
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