the GNU version of the Collaborative International Dictionary of English
n. The cooling room of the Roman thermæ, furnished with a cold bath.
The Century Dictionary and Cyclopedia
n. In ancient architecture, the cooling-apartment in a bath, in or adjoining which the cold bath was placed.
Word Usage
"They also found a "frigidarium" - a cold pool that was part of the baths built into the exclusive complex located just by the Forum constructed by Emperor Trajan."