faithlessly

faith·less  (fthls)

adj.

1. Not true to duty or obligation; disloyal.

2. Having no religious faith.

3. Unworthy of faith or trust; unreliable.

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faithless·ly adv.

faithless·ness n.

Synonyms: faithless, unfaithful, false, disloyal, traitorous, treacherous, perfidious
These adjectives mean not true to duty or obligation. Faithless and unfaithful imply failure to adhere to promises, obligations, or allegiances: was faithless to her ideals; an unfaithful spouse.
False emphasizes deceitfulness: "To thine own self be true,/And it must follow, as the night the day,/Thou canst not then be false to any man" (Shakespeare).
One who is disloyal betrays an allegiance: disloyal staff members who exposed the senator's indiscretions.
Traitorous most commonly refers to disloyalty to a government or nation: a traitorous double agent.
Treacherous suggests a propensity for betraying trust or faith: "She gave the treacherous impulse time to subside" (Henry James).
Perfidious suggests vileness of behavior and often deceitfulness: a perfidious assassin.

Thesaurus

Adv.

1.

faithlessly - in a disloyal and faithless manner; "he behaved treacherously"; "his wife played him false" false, traitorously, treacherously, treasonably