black Hollander vs osier

black Hollander and osier both are nouns.

Word	Noun	Adjective	Verb	Adverb
black Hollander	Yes	No	No	No
osier	Yes	No	No	No

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

black Hollander: Old World willow with light green leaves cultivated for use in basketry
osier: any of various willows having pliable twigs used in basketry and furniture

black Hollander (noun)	osier (noun)
Old World willow with light green leaves cultivated for use in basketry	any of various willows having pliable twigs used in basketry and furniture
	flexible twig of a willow tree