sanitarium vs infirmary

sanitarium and infirmary both are nouns.

Word	Noun	Adjective	Verb	Adverb
sanitarium	Yes	No	No	No
infirmary	Yes	No	No	No

As nouns, infirmary is a hypernym of sanitarium; that is, infirmary is a word with a broader meaning than sanitarium:

sanitarium: a hospital for recuperation or for the treatment of chronic diseases
infirmary: a health facility where patients receive treatment

Other hypernyms of sanitarium include hospital.

sanitarium (noun)	infirmary (noun)
a hospital for recuperation or for the treatment of chronic diseases	a health facility where patients receive treatment