mountain lion vs cougar

mountain lion and cougar both are nouns.

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

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

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

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