Source : Webster's Revised Unabridged Dictionary (1913)

Baptistery \Bap"tis*ter*y\,Baptistry \Bap"tis*try\, n.; pl.
   {Baptisteries}, {-tries} (?). [L. baptisterium, Gr. ?: cf. F.
   baptist[`e]re.] (Arch.)
      (a) In early times, a separate building, usually
          polygonal, used for baptismal services. Small churches
          were often changed into baptisteries when larger
          churches were built near.
      (b) A part of a church containing a font and used for
          baptismal services.