cougar vs mountain lion

cougar and mountain lion both are nouns.

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

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

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

cougar (noun)	mountain lion (noun)
large American feline resembling a lion	large American feline resembling a lion