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1. A religious rite considered a sacrament by most Christian groups, marked by the symbolic application of water to the head or immersion of the body into water and resulting in admission of the recipient into the community of Christians.
2. A ceremony in certain religious or nonreligious traditions in which one is initiated, purified, or given a name.
3. An initiatory experience, act, or effort: "two brilliant young graduate students whose work for this committee amounted to a baptism in defense policy" (James Carroll).
[Middle English baptisme, from Old French, from Late Latin baptismus, from Greek baptismos, from baptizein, to baptize; see baptize.]