Faithless

1. Not believing; not giving credit.
2. Not believing on God or religion; specifically, not believing in the Christian religion.
3. Not true to allegiance, duty, or vows; perfidious; trecherous; disloyal; not of true fidelity; inconstant, as a husband or a wife.
4. Not observant of promises or covenants.
5. Serving to disappoint or deceive; delusive; unsatisfying.