silver willow vs willow

silver willow and willow both are nouns.

Word	Noun	Adjective	Verb	Adverb
silver willow	Yes	No	No	No
willow	Yes	No	No	No

As nouns, willow is a hypernym of silver willow; that is, willow is a word with a broader meaning than silver willow:

silver willow: North American willow with greyish silky pubescent leaves that usually blacken in drying
willow: any of numerous deciduous trees and shrubs of the genus Salix

Other hypernyms of silver willow include willow tree.

silver willow (noun)	willow (noun)
North American willow with greyish silky pubescent leaves that usually blacken in drying	a textile machine having a system of revolving spikes for opening and cleaning raw textile fibers
	any of numerous deciduous trees and shrubs of the genus Salix