Illicit sex relations outside of Scriptural marriage. The Hebrew verb za·nahʹ and its related forms convey the idea of harlotry, immoral intercourse, fornication, or prostitution. (Ge 38:24; Ex 34:16; Ho 1:2; Le 19:29) The Greek word translated “fornication” is por·neiʹa. Regarding the meanings of por·neiʹa, B. F. Westcott in his book Saint Paul’s Epistle to the Ephesians (1906, p. 76) says: “This is a general term for all unlawful intercourse, (I) adultery: Hos. ii. 2, 4 (LXX.); Matt. v. 32; xix. 9; (2) unlawful marriage, I Cor. v. I; (3) fornication, the common sense as here [Eph 5:3].” Bauer’s Greek-English Lexicon of the New Testament (revised by F. W. Gingrich and F. Danker, 1979, p. 693) defines por·neiʹa as “prostitution, unchastity, fornication, of every kind of unlawful sexual intercourse.” Porneia is understood to involve the grossly immoral use of the genital organ(s) of at least one human; also there must have been two or more parties (including another consenting human or a beast), whether of the same sex or the opposite sex. (Jude 7) The unlawful act of a rapist is fornication, but, of course, that does not make the person who is forcibly raped also a fornicator.

The apostle Paul points out that fornication is one of the works of the flesh, the opposite of the fruitage of the spirit of God, and warns that the practice of fleshly works will prevent an individual from inheriting the Kingdom. (Ga 5:19-21) He counsels that the Christian should deaden his body “as respects fornication.” (Col 3:5) In fact, he warns that it should not even be a topic of conversation among Christians, who should be holy. Similarly, the Israelites were not to mention the names of the pagan gods​—not that they would fail to warn their children about these gods, but they would not mention them with any esteem.​—Eph 5:3; Ex 23:13.