osier vs willow tree

osier and willow tree both are nouns.

Word	Noun	Adjective	Verb	Adverb
osier	Yes	No	No	No
willow tree	Yes	No	No	No

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

osier: any of various willows having pliable twigs used in basketry and furniture
willow tree: any of numerous deciduous trees and shrubs of the genus Salix

Other hypernyms of osier include willow.

osier (noun)	willow tree (noun)
any of various willows having pliable twigs used in basketry and furniture	any of numerous deciduous trees and shrubs of the genus Salix
flexible twig of a willow tree