black hickory vs walnut tree

black hickory and walnut tree both are nouns.

Word	Noun	Adjective	Verb	Adverb
black hickory	Yes	No	No	No
walnut tree	Yes	No	No	No

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

black hickory: North American walnut tree with hard dark wood and edible nut
walnut tree: any of various trees of the genus Juglans

Other hypernyms of black hickory include walnut.

black hickory (noun)	walnut tree (noun)
an American hickory tree having bitter nuts	any of various trees of the genus Juglans
smooth-barked North American hickory with 7 to 9 leaflets bearing a hard-shelled edible nut
North American walnut tree with hard dark wood and edible nut