butternut tree vs walnut

butternut tree and walnut both are nouns.

Word	Noun	Adjective	Verb	Adverb
butternut tree	Yes	No	No	No
walnut	Yes	No	No	No

As nouns, walnut is a hypernym of butternut tree; that is, walnut is a word with a broader meaning than butternut tree:

butternut tree: North American walnut tree having light-brown wood and edible nuts; source of a light-brown dye
walnut: any of various trees of the genus Juglans

Other hypernyms of butternut tree include walnut tree.

butternut tree (noun)	walnut (noun)
North American walnut tree having light-brown wood and edible nuts; source of a light-brown dye	nut of any of various walnut trees having a wrinkled two-lobed seed with a hard shell
	any of various trees of the genus Juglans
	hard dark-brown wood of any of various walnut trees; used especially for furniture and paneling