The Collaborative International Dictionary
Frigidarium \Frig"i*da`ri*um\, n.; pl. Frigidaria. [L., neut. of frigidarium cooling.] The cooling room of the Roman therm[ae], furnished with a cold bath.
Wikipedia
A frigidarium is a large cold pool at the Roman baths. It would be entered after the caldarium and the tepidarium, which were used to open the pores of the skin. The cold water would close the pores. There would be a small pool of cold water or sometimes a large swimming pool (though this, differently from the piscina natatoria, was usually covered). The water could be also kept cold by using snow.
The frigidarium was usually located on the northern side of the baths. The largest examples of frigidarium were both in Rome: that of the Baths of Caracalla, located soon after the entrance, measures 58 x 24 m, and that of the Baths of Diocletian, covered by a cross vault. Some, like one in Pompeii, had a circular plan.
Usage examples of "frigidarium".
Lenardo could hear their voices echoing down the hall and the shouts and splashes as they jumped into the frigidarium pool.
Unlike the small bathhouse at the Academy, this one had a frigidarium pool big enough to swim in.
Thence, stark-naked, through the bronze doors set in greenveined marble, bathers passed into the vast frigidarium, whose marble plunge was surrounded by a mosaic promenade beneath a bronze and marble balcony.
Pertinax looked at the bronze door leading to the sweating room, shrugging himself as if the frigidarium had grown too cool for comfort.
Harben enjoyed the prospect of a swim in the clear, cold water of the frigidarium, he was much more interested by the opportunity it afforded him to be with Favonia again.
Fupus, who had entered the frigidarium behind von Harben, sneered as he saw the dive and heard the applause.
Lusty shouts rang out as men indulged in a game of toss-the-ball in the more bracing frigidarium adjoining.
Then we went to the tepidarium and splashed about in pools of gradually decreasing warmth, until we were able, without too great a shock, to plunge into the chilly pool of the frigidarium.