purple osier vs osier

purple osier and osier both are nouns.

Word	Noun	Adjective	Verb	Adverb
purple osier	Yes	No	No	No
osier	Yes	No	No	No

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

purple osier: Eurasian osier having reddish or purple twigs and bark rich in tannin
osier: any of various willows having pliable twigs used in basketry and furniture

purple osier (noun)	osier (noun)
Eurasian osier having reddish or purple twigs and bark rich in tannin	any of various willows having pliable twigs used in basketry and furniture
	flexible twig of a willow tree