1. An unlawful commerce between one married person and another, or between a married and an unmarried person.
2. It is also used in Scripture for idolatry, or departing from the true God. Jeremiah 3:9 .
3. Also for any species of impurity or crime against the virtue of chastity. Matthew 5:28 .
4. It is also used in ecclesiastical writer's for a person's invading or intruding into a bishoprick during the former bishop's life.
5. The word is also used in ancient customs for the punishment or fine imposed for that offence, or the privilege of prosecuting for it.
Although adultery is prohibited by the law of God, yet some have endeavored to explain away the moral turpitude of it; but it is evident, observes Paley, that, on the part of the man who solicits the chastity of a married woman, it certainly includes the crime of seduction, and is attended with mischief still more extensive and complicated: it creates a new sufferer, the injured husband, upon whose affection is inflicted a wound the most painful and incurable that human nature knows. The infidelity of the woman is aggravated by cruelty to her children, who are generally involved in their parents' shame, and always made unhappy by their quarrel. The marriage vow is witnessed before God, and accompanied with circumstances of solemnity and religion, which approach to the nature of an oath. The married offender, therefore, incurs a crime little short of perjury, and the seduction of a married woman is little less than subornation of perjury. But the strongest apology for adultery is, the prior transgression of the other party; and so far, indeed, as the bad effects of adultery are anticipated by the conduct of the husband or wife who offends first, the guilt of the second offender is extenuated.
But this can never amount to a justification, unless it could be shown that the obligation of the marriage vow depends upon the condition of reciprocal fidelity; a construction which appears founded neither in expediency, nor in terms of the vow, nor in the design of the legislature, which prescribed the marriage rite. To consider the offence upon the footing of provocation, therefore, can by no means vindicate retaliation. "Thou shalt not commit adultery, " it must ever be remembered, was an interdict delivered by God himself. This crime has been punished in almost all ages and nations. By the Jewish law it was punished with death in both parties, where either the woman was married, or both. Among the Egyptians, adultery in the man was punished by a thousand lashes with rods, and in the woman by the loss of her nose. The Greeks put out the eyes of the adulterers. Among the Romans, it was punished by banishment, cutting off the ears, noses, and by sewing the adulterers into sacks, and throwing them into the sea, scourging, burning, &c. In Spain and Poland they were almost as severe. The Saxons formerly burnt the adulteress, and over her ashes erected a gibbet, whereon the adulterer was hanged. King Edmund in this kingdom, ordered adultery to be punished in the same manner as homicide. Canute ordered the man to be banished, and the woman to have her nose and ears cut off. Modern punishments, in different nations, do not seem to be so severe. In Britain it is reckoned a spiritual offence, and is cognizable by the spiritual courts, where it is punished by fine and penance.
See Paley's Moral and Political Philosophy, p. 309, vol. 1: 12th edition.