FORNICATION

At one time, the unlawful carnal knowledge of an unmarried person with another, whether the latter be married or unmarried. When the party is married, the offence, as to him or her, is known by the name of adultery. However, fornication is included in every case of adultery, as a larceny is included in robbery.

Currently, the term is used to refer to sexual intercourse in the general sense, whether lawful or not.
   

This entry contains material from Bouvier's Legal Dictionary, a work published in the 1850's.