Etymology
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unfaithful (adj.)

mid-14c., "acting falsely," from un- (1) "not" + faithful. In Middle English it had also a sense of "infidel, unbelieving, irreligious" (late 14c.). The meaning "not faithful in marriage" is attested from 1828. Related: Unfaithfully; unfaithfulness.

updated on March 30, 2022

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