baptism

n. ceremonial immersion into water, initiatory rite of the Christian Church; purification by submergence

Baptism, from Greek  (baptízô), is a religious act of purification by water usually associated with admission to membership or fullness of membership of Christianity.The Greek-English Lexicon of Liddell and Scott gives the primary meaning of the word , from which the English word baptism is derived, as dip, plunge, but indicates, citing , that it was used also to mean perform ablutions.By analogy, the English word "baptism" is used of any ceremony, trial, or experience by which one is initiated, purified, or given a name. See Other initiation ceremonies below.
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Noun
1. a Christian sacrament signifying spiritual cleansing and rebirth; "most churches baptize infants but some insist on adult baptism"
(hypernym) sacrament
(hyponym) affusion
(derivation) baptize, baptise, christen

(v. i.)
The act of baptizing; the application of water to a person, as a sacrament or religious ceremony, by which he is initiated into the visible church of Christ. This is performed by immersion, sprinkling, or pouring.
  

Baptism [from Greek baptizein to sprinkle] Ceremonial of purification with water; one of the sacraments in the Christian churches, by which persons are initiated into the visible Church of Christ. It consists in either immersion in water or sprinkling with water, according to the practice of different churches. In the Protestant Churches it is "the outward and visible sign of an inward and spiritual grace," accepted as a necessary preliminary to the other sacraments, and even as essential to salvation. In the Roman Catholic Church it carries remission of sin both original and actual. It existed in pre-Christian times among Jews and pagans, practiced in Chaldea, Egypt, India, Greece, Africa, Polynesia, North America, and ancient Europe, among others.
Mystically speaking, there are two baptisms: that of water and that of fire; the former pertaining to the plane of matter, the latter to that of spirit. In the New Testament, John the Baptist says: "I baptize you with water, but a greater than I shall come, who will baptize you with fire." Jesus instructs Nicodemus as to the two births: the birth of water and the birth of the spirit. Baptism was therefore a ceremonial pertaining to an inferior degree of initiation.