Source : Webster's Revised Unabridged Dictionary (1913)

Infidelity \In`fi*del"i*ty\, n.; pl. {Infidelities}. [L.
   infidelitas: cf. F. infid['e]lit['e].]
   1. Want of faith or belief in some religious system;
      especially, a want of faith in, or disbelief of, the
      inspiration of the Scriptures, of the divine origin of
      Christianity.

            There is, indeed, no doubt but that vanity is one of
            the principal causes of infidelity.   --V. Knox.

   2. Unfaithfulness to the marriage vow or contract; violation
      of the marriage covenant by adultery.

   3. Breach of trust; unfaithfulness to a charge, or to moral
      obligation; treachery; deceit; as, the infidelity of a
      servant. ``The infidelity of friends.'' --Sir W. Temple.