pussy willow vs genus Salix

pussy willow and genus Salix both are nouns.

Word	Noun	Adjective	Verb	Adverb
pussy willow	Yes	No	No	No
genus Salix	Yes	No	No	No

pussy willow (noun)	genus Salix (noun)
small willow of eastern North America having greyish leaves and silky catkins that come before the leaves	a large and widespread genus varying in size from small shrubs to large trees: willows
much-branched Old World willow having large catkins and relatively large broad leaves