The Collaborative International Dictionary of English v.0.48:

Infidelity \In`fi*del"i*ty\, n.; pl. Infidelities. [L.
   infidelitas: cf. F. infid['e]lit['e].]
   [1913 Webster]
   1. Lack of faith or belief in some religious system;
      especially, a lack of faith in, or disbelief of, the
      inspiration of the Scriptures, of the divine origin of
      Christianity.
      [1913 Webster]

            There is, indeed, no doubt but that vanity is one of
            the principal causes of infidelity.   --V. Knox.
      [1913 Webster]

   2. Unfaithfulness to the marriage vow or contract; violation
      of the marriage covenant by adultery.
      [1913 Webster]

   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.
      [1913 Webster]