This word is acceptable for play in the US & UK dictionaries that are being used in the following games:

• Lexulous
• Wordscraper
• Wordosaur

n. In Roman baths, the hottest room, with a plunge-pool. It preceded the tepidarium and frigidarium.

n. In modern spas, a room with a hot floor.

n. The Roman name for a stove or heating apparatus.

n. A room in the Roman thermæ, or public baths, in which water was heated to the highest temperature. See bath, 5.

"The Roman-style baths include an apodypterium , or changing room; a tepidarium , or warm room; and a caldarium , or hot room, along with a domed chamber for housing firewood."