purple mullein vs velvet plant

purple mullein and velvet plant both are nouns.

Word	Noun	Adjective	Verb	Adverb
purple mullein	Yes	No	No	No
velvet plant	Yes	No	No	No

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

purple mullein: Eurasian mullein with showy purple or pink flowers
velvet plant: any of various plants of the genus Verbascum having large usually woolly leaves and terminal spikes of yellow or white or purplish flowers

Other hypernyms of purple mullein include flannel leaf, mullein.

purple mullein (noun)	velvet plant (noun)
Eurasian mullein with showy purple or pink flowers	Javanese foliage plant grown for their handsome velvety leaves with violet-purple hairs
	any of various plants of the genus Verbascum having large usually woolly leaves and terminal spikes of yellow or white or purplish flowers