Juglans regia vs walnut

Juglans regia and walnut both are nouns.

Word	Noun	Adjective	Verb	Adverb
Juglans regia	Yes	No	No	No
walnut	Yes	No	No	No

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

Juglans regia: Eurasian walnut valued for its large edible nut and its hard richly figured wood; widely cultivated
walnut: any of various trees of the genus Juglans

Other hypernyms of Juglans regia include walnut tree.

Juglans regia (noun)	walnut (noun)
Eurasian walnut valued for its large edible nut and its hard richly figured wood; widely cultivated	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