walnut tree vs walnut

walnut tree and walnut both are nouns.

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

As nouns, walnut tree and walnut are synonyms defined as:

walnut tree (noun)	walnut (noun)
any of various trees of the genus Juglans	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