1. (a.) 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.

2. (a.) Not possessing faith; infidel.

derelict disaffected disloyal disregardful faithless FALSE fickle inattentive inconstant inobservant negligent nonadherent noncompliant nonconforming nonobservant not true to of bad faith perfidious recreant traitorous treacherous trothless uncompliant unconforming unloyal unobservant unsteadfast untrue