faithless
— Adjective
– English
~ having the character of, or characteristic of, a traitor; "the faithless Benedict Arnold"; "a lying traitorous insurrectionist"
faithlessly
— Adverb
– English
~ in a disloyal and faithless manner; "he behaved treacherously"; "his wife played him false"
faithlessness
— Noun
– English
~ unfaithfulness by virtue of being unreliable or treacherous