Adultery is the violation of the marriage covenant by sexual union with someone other than one's spouse. It is categorically forbidden in the Seventh Commandment (Exod 20:14) and treated throughout Scripture as both a personal transgression and a spiritual metaphor. God repeatedly describes Israel's idolatry as spiritual adultery — whoring after foreign gods while covenanted to Yahweh (Jer 3:8–9; Ezek 16; Hos 1–3). Jesus intensified the prohibition: adultery begins in the heart through lustful intent (Matt 5:28), not merely in the physical act. The NT lists it among the works of the flesh that exclude from the kingdom (Gal 5:19–21). Yet Scripture also presents the profound grace of redemption for the adulterer — the woman caught in adultery met the one who refused to condemn but also commanded, "Go and sin no more" (John 8:11).
ADUL'TERY, n. [L. adulterium.] Violation of the marriage bed; a crime, or a civil injury, which introduces, or may introduce, into a family, a spurious offspring. By the laws of Connecticut, the sexual intercourse of any man, with a married woman, is the crime of adultery in both: Such intercourse of a married man with an unmarried woman, is fornication in both, and adultery of the man in the sense of Scripture and ecclesiastical law. In Scripture, it means idolatry, or apostasy from the true God. — Noah Webster, 1828
• Exodus 20:14 — "You shall not commit adultery."
• Matthew 5:27–28 — "Everyone who looks at a woman with lustful intent has already committed adultery with her in his heart."
• John 8:10–11 — "Neither do I condemn you; go, and from now on sin no more."
• Hebrews 13:4 — "Let marriage be held in honor among all, and let the marriage bed be undefiled, for God will judge the sexually immoral and adulterous."
• Jeremiah 3:8 — "I gave faithless Israel her certificate of divorce…yet her unfaithful sister Judah had no fear — she also went out and committed adultery."
G3430 — moicheia (μοιχεία): adultery, marital unfaithfulness; one of the vices listed in Matt 15:19 as proceeding from the heart.
G3431 — moicheuo (μοιχεύω): to commit adultery; used in the Seventh Commandment citation and the Sermon on the Mount.
H5003 — na'aph (נָאַף): to commit adultery; used literally and metaphorically of Israel's spiritual unfaithfulness to Yahweh.
Latin adulterare ("to corrupt, defile, adulterate")
→ ad- ("to") + alter ("other") — to go to another
→ adulterium → Old French avouterie → Middle English adulterie
Greek: μοιχεία (moicheia) — possibly from pre-Greek Mediterranean root
→ μοιχός (moichos) — adulterer
Hebrew: נָאַף (na'aph) — Proto-Semitic root for sexual transgression
→ Noun: נֹאֵף (no'ef) — adulterer
→ Used metaphorically for covenant-breaking idolatry throughout the prophets
Modern culture has largely decriminalized and normalized adultery, treating it as a personal choice within "open relationships" or a recoverable mistake without moral weight. Affairs are romanticized in film and literature. The concept of "emotional affairs" — intimate non-sexual bonds that betray the marriage covenant — is often dismissed entirely. Scripture, however, locates adultery's root in the heart (Matt 5:28) and its scope in covenant betrayal. A culture that winks at adultery dismantles the family, which is the foundational institution of civilization and a living picture of Christ's relationship with His Church (Eph 5:31–32).