greenhouse vs hothouse

greenhouse and hothouse both are nouns.

Word	Noun	Adjective	Verb	Adverb
greenhouse	Yes	Yes	No	No
hothouse	Yes	No	No	No

As nouns, hothouse is a hyponym of greenhouse; that is, hothouse is a word with a more specific, narrower meaning than greenhouse:

greenhouse: a building with glass walls and roof; for the cultivation and exhibition of plants under controlled conditions
hothouse: a greenhouse in which plants are arranged in a pleasing manner

Other hyponyms of greenhouse include conservatory, indoor garden, orangery.

greenhouse (noun)	hothouse (noun)
a building with glass walls and roof; for the cultivation and exhibition of plants under controlled conditions	a greenhouse in which plants are arranged in a pleasing manner

greenhouse (adjective)	hothouse (adjective)
of or relating to or caused by the greenhouse effect