Source : Webster's Revised Unabridged Dictionary (1913)

Baptism \Bap"tism\, n. [OE. baptim, baptem, OE. baptesme,
   batisme, F. bapt[^e]me, L. baptisma, fr. Gr. ?, fr. ? to
   baptize, fr. ? to dip in water, akin to ? deep, Skr. g[=a]h
   to dip, bathe, 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.

Source : WordNet®

baptism
     n : a Christian sacrament signifying spiritual cleansing and
         rebirth; "most churches baptize infants but some insist
         on adult baptism"