c. 1200, "one who baptizes," also (with capital B-) a title of John, the forerunner of Christ; see baptize + -ist. As "member of a Protestant sect that believes in adult baptism upon profession of faith," generally by full immersion (with capital B-), attested from 1654; their opponents called them anabaptists (see Anabaptist).
"to administer the rite of baptism to," c. 1300, from Old French batisier "be baptized; baptize; give a name to" (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 Christian use, "baptize." This is from baptein "to dip, steep, dye, color," which is perhaps from PIE root *gwabh- (1) "to dip, sink." Christian baptism originally was a full immersion. Related: Baptized; baptizing.
"initiatory sacrament of the Christian faith, consisting in immersion in or application of water by an authorized administrator," c. 1300, bapteme, from Old French batesme, bapteme "baptism" (11c., Modern French baptême), from Latin baptismus, from Greek baptismos, noun of action from baptizein (see baptize). The -s- was restored in late 14c.
The signification, qualifications, and methods of administration have been much debated. The figurative sense of "any ceremonial ablution as a sign of purification, dedication, etc." is from late 14c. Old English used fulluht in this sense (John the Baptist was Iohannes se Fulluhtere).
Phrase baptism of fire "a soldier's first experience of battle" (1857) translates French baptême de feu; the phrase originally was ecclesiastical Greek baptisma pyros and meant "the grace of the Holy Spirit as imparted through baptism;" later it was used of martyrdom, especially by burning.