in the ancient baths, denoted a brazen vessel or cistern, placed in the hypocaustum, full of hot water, to be drawn thence into the piscina or bath, to give it the necessary degree of heat. In this sense, the caldarium stood contradistinguished from the tepidarium and frigidarium.

Caldarium also denoted the stove, or fudatory, being a close vaulted room, wherein by hot dry fumes, without water, people were brought to a profuse sweat. In which sense, caldarium was the same with what was otherwise denominated vaporarium, fudatorium, and laconium; in the Greek baths, hypocaustum, ὑπόκαυστον.