caldariums

Noun

caldarium (plural caldariums or caldaria)

1. (historical) In Roman baths, the hottest room, with a plunge-pool. It preceded the tepidarium and frigidarium.
2. In modern spas, a room with a hot floor.
3. An intermediate or warm greenhouse.
   • There is a pretty large glass-house, one-half being a caldarium, the other a tepidarium1851, The Floricultural Cabinet and Florist's Magazine, page 184