Lacking faith, loyalty, or belief; disloyal or untrustworthy, especially in relationships or religious matters.
From Middle English, combining 'faith' (from Old French 'feid', Latin 'fides' meaning trust) with the suffix '-less' indicating absence or lack.
Interestingly, 'faithless' can describe both religious doubt and romantic betrayal, showing how the concept of faith bridges spiritual and personal relationships - both requiring the same fundamental trust in something beyond immediate proof.
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