blacksnake vs rat snake

blacksnake and rat snake both are nouns.

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

As nouns, rat snake is a hypernym of blacksnake; that is, rat snake is a word with a broader meaning than blacksnake:

blacksnake: large harmless shiny black North American snake
rat snake: any of various nonvenomous rodent-eating snakes of North America and Asia

blacksnake (noun)	rat snake (noun)
blackish racer of the eastern United States that grows to six feet	any of various nonvenomous rodent-eating snakes of North America and Asia
large harmless shiny black North American snake