Lewis & Short

† hypŏcaustum or -on, i, n., = ὑπόκαυστον,

  1. I. a bathing-room heated from below, a sweating-chamber (pure Lat. vaporarium), Vitr. 5, 10; Plin. Ep. 2, 17, 23; 11; Stat. S. 1, 5, 59; Dig. 17, 1, 16 al.
  2. II. Adj.: diaetae hypocaustae, sweating-rooms, Dig. 32, 9, 55, § 3.