baptize: [13] The underlying notion of baptize is of ‘dipping’, as those baptized were originally (and sometimes still are) immersed in water. It comes from Greek báptein ‘dip’, whose derivative baptízein ‘baptize’ passed via Latin baptizāre and Old French baptiser into English. Old Norse kafa ‘dive’ is a Germanic relative.
c. 1300, from Old French batisier (11c.), from Latin baptizare, from Greek baptizein "immerse, dip in water," also figuratively, "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.