Source : Webster's Revised Unabridged Dictionary (1913)

Adultery \A*dul"ter*y\, n.; pl. {Adulteries}. [L. adulterium.
   See {Advoutry}.]
   1. The unfaithfulness of a married person to the marriage
      bed; sexual intercourse by a married man with another than
      his wife, or voluntary sexual intercourse by a married
      woman with another than her husband.

Source : WordNet®

adultery
     n : extramarital sex that willfully and maliciously interferes
         with marriage relations; "adultery is often cited as
         grounds for divorce" [syn: {criminal conversation}, {fornication}]