shellbark vs hickory tree

shellbark and hickory tree both are nouns.

Word	Noun	Adjective	Verb	Adverb
shellbark	Yes	No	No	No
hickory tree	Yes	No	No	No

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

shellbark: North American hickory having loose grey shaggy bark and edible nuts
hickory tree: American hardwood tree bearing edible nuts

Other hypernyms of shellbark include hickory.

shellbark (noun)	hickory tree (noun)
North American hickory having loose grey shaggy bark and edible nuts	American hardwood tree bearing edible nuts