Definitions for faithlessly
Random House Webster's College Dictionary
not adhering to allegiance, promises, vows, or duty.
not trustworthy; unreliable.
lacking trust or belief, esp. without religious faith.
Origin of faithless:
faithlessly, traitorously, treacherously, treasonably, false(adverb)
in a disloyal and faithless manner
"he behaved treacherously"; "his wife played him false"
In a faithless manner