The word Hypocaust refers to a system of central heating in which hot air flows through spaces under the floor of a room. If you're looking for synonyms for this word, there are several options. One such synonym is "underfloor heating," which refers to a heating system that is installed below the surface of the floor. Another synonym is "hypokauston," which is a Greek word that means exactly the same thing as Hypocaust. Other synonyms for Hypocaust include "heated flooring," "floor heating," and "radiant heating." If you're writing about ancient Rome, you might also use the Latin term "praefurnium," which describes the furnace that was used to heat the air in a Hypocaust system.