copperhead vs pit viper

copperhead and pit viper both are nouns.

Word	Noun	Adjective	Verb	Adverb
copperhead	Yes	No	No	No
pit viper	Yes	No	No	No

As nouns, pit viper is a hypernym of copperhead; that is, pit viper is a word with a broader meaning than copperhead:

copperhead: common coppery brown pit viper of upland eastern United States
pit viper: New World vipers with hollow fangs and a heat-sensitive pit on each side of the head

copperhead (noun)	pit viper (noun)
common coppery brown pit viper of upland eastern United States	New World vipers with hollow fangs and a heat-sensitive pit on each side of the head
venomous but sluggish reddish-brown snake of Australia