Source : Webster's Revised Unabridged Dictionary (1913)

Fornication \For`ni*ca"tion\, n. [F. fornication, L.
   fornicatio.]
   1. Unlawful sexual intercourse on the part of an unmarried
      person; the act of such illicit sexual intercourse between
      a man and a woman as does not by law amount to adultery.

   Note: In England, the offense, though cognizable in the
         ecclesiastical courts, was not at common law subject to
         secular prosecution. In the United States it is
         indictable in some States at common law, in others only
         by statute. --Whartyon.

   2. (Script.)
      (a) Adultery.
      (b) Incest.
      (c) Idolatry.

Source : WordNet®

fornication
     n 1: voluntary sexual intercourse between persons not married to
          each other
     2: extramarital sex that willfully and maliciously interferes
        with marriage relations; "adultery is often cited as
        grounds for divorce" [syn: {adultery}, {criminal
        conversation}]