black rat snake vs mountain blacksnake

black rat snake and mountain blacksnake both are nouns.

Word	Noun	Adjective	Verb	Adverb
black rat snake	Yes	No	No	No
mountain blacksnake	Yes	No	No	No

As nouns, black rat snake and mountain blacksnake are synonyms defined as:

black rat snake and mountain blacksnake: large harmless shiny black North American snake

Other synonyms of black rat snake include blacksnake, Elaphe obsoleta, pilot blacksnake.

black rat snake (noun)	mountain blacksnake (noun)
large harmless shiny black North American snake	large harmless shiny black North American snake