velvet plant vs houseplant

velvet plant and houseplant both are nouns.

Word	Noun	Adjective	Verb	Adverb
velvet plant	Yes	No	No	No
houseplant	Yes	No	No	No

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

velvet plant: Javanese foliage plant grown for their handsome velvety leaves with violet-purple hairs
houseplant: any of a variety of plants grown indoors for decorative purposes

velvet plant (noun)	houseplant (noun)
Javanese foliage plant grown for their handsome velvety leaves with violet-purple hairs	any of a variety of plants grown indoors for decorative purposes
any of various plants of the genus Verbascum having large usually woolly leaves and terminal spikes of yellow or white or purplish flowers