Unfaithful

Part of speech: adjective (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.] Milton. -- Un*faith"ful*ly, adv. -- Un*faith"ful*ness, n.