commit (fornication)

Boyd’s Bible Dictionary:

(crime under the arch). Crime of impurity between unmarried persons. Figuratively, infidelity to God (Ezek. 16:2; Jer. 2:20; Matt. 5:32).

Concise Bible Dictionary:

This was very common among the Gentiles, which accounts for its being mentioned in the message sent from the conference at Jerusalem to the Gentiles (Acts 15:20, 29); and its being so often prohibited in the epistles. The word is sometimes used where “adultery” is the sense (Matt. 5:32; Matt. 19:9). It often has in the O. T. a symbolical reference to the turning from God to idols (2 Chron. 21:11, 13; Isa. 23:17; Ezek. 16:15, 26, 29); and in the N. T. to unfaithful intercourse with Babylon, the mother of harlots (Rev. 14:8; Rev. 17:2, 4; Rev. 18:3, 9).

Strong’s Dictionary of Greek Words:

from 4204; to act the harlot, i.e. (literally) indulge unlawful lust (of either sex), or (figuratively) practise idolatry
KJV Usage:
commit (fornication)