What is the X in X-mas?
c.1300, from Old French batisier (11c.), from Latin baptizare, from Greek baptizein "to immerse, to dip in water," also used figuratively, e.g. "to be over one's head" (in debt, etc.), "to be soaked (in wine);" in Greek Christian usage, "baptize;" from baptein "to dip, steep, dye, color," from PIE root *gwabh- "to dip, sink." Christian baptism originally consisted in full immersion. Related: Baptized; baptizing.