Webster's Dictionary 
(n.) Alt. of Baptistry
Cyclopedia of Biblical, Theological and Ecclesiastical Literature 
a place or room set apart for performing baptism. We have no account in the New Testament of any such separated places. John and the disciples of our Lord Jesus Christ baptized in the Jordan. But baptism could be administered in other places (see Acts 8:36-37; Acts 16:13-16). There was a public baptism of three thousand converts on the day of Pentecost ( Acts 2:41), but no account is given of the place. Examples also occur in the Acts of the Apostles of baptism in private houses. Passages in the writings of Justin Martyr, Clement, and Tertullian show that, during their time, there were no baptisteries. In later times the baptistery was one of the exedrae, or buildings distinct from the church itself, and consisted of the porch, where the person about to be baptized made the confession of faith, and an inner room, where the ceremony was performed. Thus it remained till the sixth century, when the baptistery was taken into the church porch, and afterward into the church itself. The ancient baptisteries were sometimes called Φωτιστήρια ( Illuminatoria ) , either because baptism was sometimes called Φωτισμός , Illumination, or because they were places of illumination or instruction, preceding baptism, where the catechumens were taught the first principles of the Christian faith. We occasionally meet with the word Κολυμβήθρα or Piscina (the font). The octagonal or circular form was adopted, surmounted with a dome, and the baptistery was situated at the entrance to the principal or western gate. These edifices are of considerable antiquity, since one was prepared for the ceremonial of the baptism of Clovis. It is not possible to decide at what period they began to be multiplied, and at length united to, or changed into parish churches; yet it appears that the alteration took place when stated seasons of baptism ceased, and the right of administration was ceded to all presbyters and deacons. The word baptistery is now applied also to the baptismal font. — Bingham, Orig. Eccles. bk. 8, ch. 7, § 1-4.