society > morality > moral evil > licentiousness > unchastity > fornication, adultery, or incest > commit fornication, adultery, or incest [verb (intransitive)] > fornicate (4)
intransitive for reflexive. (Often conjugated with be). To commit fornication. Const. by or with.
intransitive. To transgress, err; to commit a sin or misdeed, spec. to fornicate.
intransitive. To commit fornication.
By Skene associated with French forfaire, medieval Latin forisfacĕre. (See quot.)