What is the X in X-mas?
c.1400, from Late Latin fomentationem, noun of action from past participle stem of fomentare, from Latin fomentum (see foment).
fomentation fo·men·ta·tion (fō'mən-tā'shən, -měn-)n.
A substance or material used as a warm, moist medicinal compress; a poultice.
The therapeutic application of warmth and moisture, as to relieve pain.