dwarf grey willow vs willow

dwarf grey willow and willow both are nouns.

Word	Noun	Adjective	Verb	Adverb
dwarf grey willow	Yes	No	No	No
willow	Yes	No	No	No

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

dwarf grey willow: willow shrub of dry places in the eastern United States having long narrow leaves canescent beneath
willow: any of numerous deciduous trees and shrubs of the genus Salix

Other hypernyms of dwarf grey willow include willow tree.

dwarf grey willow (noun)	willow (noun)
willow shrub of dry places in the eastern United States having long narrow leaves canescent beneath	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