Adultery: conjugal infidelity. An adulterer was a man who had illicit intercourse with a married or a betrothed woman, and such a woman was an adulteress. Intercourse between a married man and an unmarried woman was fornication. Adultery was regarded as a great social wrong, as well as a great sin.

The Mosaic law (Num. 5:11-31) prescribed that the suspected wife should be tried by the ordeal of the "water of jealousy." There is, however, no recorded instance of the application of this law. In subsequent times the Rabbis made various regulations with the view of discovering the guilty party, and of bringing about a divorce. It has been inferred from John 8:1-11 that this sin became very common during the age preceding the destruction of Jerusalem.

Idolatry, covetousness, and apostasy are spoken of as adultery spiritually (Jer. 3:6, 8, 9; Ezek. 16:32; Hos. 1:2:3; Rev. 2:22). An apostate church is an adulteress (Isa. 1:21; Ezek. 23:4, 7, 37), and the Jews are styled "an adulterous generation" (Matt. 12:39). (Compare Rev. 12.)