HYPPOCAUSTUM, among the Greeks and Romans, a subterraneous place, where was a furnace to heat the baths. The word is Greek, formed of the preposition υπο, under; and the verb καω, to burn.—Another sort of hypocaustum was a kind of kiln to heat their winter parlours. The remains of a Roman hypocaustum, or sweating-room, were discovered under ground at Lincoln in 1739. We have an account of these remains in the Philosophical Transactions, No 461. § 29.—Among the moderns, the hypocaustum is that place where the fire is kept which warms a stove or hot-house.