(in an ancient Roman bath) a room having a hot bath.
Origin
1745-55; < Latin: noun use of neuter of caldārius of warming, equivalent to cal(i)d(us) warm (cal(ēre) to be warm + -idus-id4) + -ārius-ary; see -ium, -arium
British Dictionary definitions for caldarium
caldarium
/kælˈdɛərɪəm/
noun (pl) -daria (-ˈdɛərɪə)
1.
(in ancient Rome) a room for taking hot baths
Word Origin
C18: from Latin, from calidus warm, from calēre to be warm