fornication (n.) Look up fornication at Dictionary.com
c.1300, from Old French fornicacion (12c.), from Late Latin fornicationem (nominative fornicatio), noun of action from past participle stem of fornicari "fornicate," from Latin fornix (genitive fornicis) "brothel" (Juvenal, Horace), originally "arch, vaulted chamber" (Roman prostitutes commonly solicited from under the arches of certain buildings), from fornus "oven of arched or domed shape." Strictly, "voluntary sex between an unmarried man and an unmarried woman;" extended in the Bible to adultery.