brittle willow vs willow

brittle willow and willow both are nouns.

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

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

brittle willow: large willow tree with stiff branches that are easily broken
willow: any of numerous deciduous trees and shrubs of the genus Salix

Other hypernyms of brittle willow include willow tree.

brittle willow (noun)	willow (noun)
large willow tree with stiff branches that are easily broken	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