The usual form of baptism among the earliest Christians involved the candidate's immersion, either totally (submerged completely under the water) or partially (standing or kneeling in water while water was poured on him or her).[a] John the Baptist's use of a deep river for his baptising suggests immersion:
The fact that he chose a permanent and deep river suggests that more than a token quantity of water was needed, and both the preposition 'in' (the Jordan) and the basic meaning of the verb 'baptize' probably indicate immersion. In v. 16, Matthew will speak of Jesus 'coming up out of the water'. Phillip and the Eunuch also went down and came up out of water (Acts 8:38–39). Baptism is likened unto a burial in Romans 6:3. "Dip" is translated from baptō (βάπτω). The traditional depiction in Christian art of John the Baptist pouring water over Jesus' head may therefore be based on later Christian practice.
Pictorial and archaeological evidence of Christian baptism from the 3rd century onward indicates that a normal form was to have the candidate stand in water while water was poured over the upper body. Other common forms of baptism now in use include pouring water three times on the forehead, a method called affusion.
Martyrdom was identified early in Church history as "baptism by blood", enabling the salvation of martyrs who had not been baptized by water. Later, the Catholic Church identified a baptism of desire, by which those preparing for baptism who die before actually receiving the sacrament are considered saved. As evidenced also in the common Christian practice of infant baptism, Christians universally regarded baptism as in some sense necessary for salvation, until Huldrych Zwingli (1484–1531) denied its necessity in the 16th century.
The English word baptism is derived indirectly through Latin from the neuter Greek concept noun baptisma (Greek βάπτισμα, "washing-ism"),[c] which is a neologism in the New Testament derived from the masculine Greek noun baptismos (βαπτισμός), a term for ritual washing in Greek language texts of Hellenistic Judaism during the Second Temple period, such as the Septuagint. Both of these nouns are derived from the verb baptizō (βαπτίζω, "I wash" transitive verb), which is used in Jewish texts for ritual washing, and in the New Testament both for ritual washing and also for the apparently new rite of baptisma. The Greek verb baptō (βάπτω), "dip", from which the verb baptizo is derived, is in turn hypothetically traced to a reconstructed Indo-European root *gʷabh-, "dip". The Greek words are used in a great variety of meanings.