Unfaithful
Unfaithful , adjective
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.
His honor rooted in dishonor stood,
And faith unfaithful kept him falsely true.
2.
Not possessing faith; infidel. [Rare] — Milton