vapor bath vs sauna

vapor bath and sauna both are nouns.

Word	Noun	Adjective	Verb	Adverb
vapor bath	Yes	No	No	No
sauna	Yes	No	No	No

As nouns, sauna is a hyponym of vapor bath; that is, sauna is a word with a more specific, narrower meaning than vapor bath:

vapor bath: a room that can be filled with steam in which people bathe; `vapour bath' is a British term
sauna: a Finnish steam bath; steam is produced by pouring water over heated rocks

Other hyponyms of vapor bath include sweat room, Turkish bath.

vapor bath (noun)	sauna (noun)
you sweat in a steam room before getting a rubdown and cold shower	a Finnish steam bath; steam is produced by pouring water over heated rocks
a room that can be filled with steam in which people bathe; `vapour bath' is a British term