Un·faith·ful a.
  1. Not faithful; not observant of promises, vows, allegiance, or duty; violating trust or confidence; treacherous; perfidious; as, an unfaithful subject; an unfaithful agent or servant.
     My feet, through wine, unfaithful to their weight.   --Pope.
  His honor rooted in dishonor stood,
  And faith unfaithful kept him falsely true.   --Tennyson.
  2. Not possessing faith; infidel. [R.]
  -- Un*faith*ful*ly, adv. -- Un*faith*ful*ness, n.
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  unfaithfulness
       n : the quality of being unfaithful [syn: infidelity] [ant: fidelity,
            fidelity]