tepidarium

/T EH1 P AH0 D EH1 R IY0 AH0 M/
noun
  1. 1

    A warm room in a Roman baths that was usually heated by a hypocaust.

  2. 2

    A boiler in which the water was heated.

  3. 3

    Any room containing a warm bath.

Source: https://en.wiktionary.org/wiki/tepidarium