{ n.; pl. Baptisteries Baptistries [ L. baptisterium, Gr. baptisth`rion: cf. F. baptistère. ] (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. [ 1913 Webster ]