UNFAITHFUL a. 2 definitions
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.
UN- n.
express the absence of, or the contrary of, that which the noun signifies; as, unbelief, unfaith, unhealth, unrest, untruth, and the like.