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[uhn-feyth-fuh l] /ʌnˈfeɪθ fəl/
not faithful; false to duty, obligation, or promises; faithless; disloyal.
not sexually faithful to a spouse or lover.
not accurate or complete; inexact:
an unfaithful translation.
Obsolete. unbelieving; infidel.
Origin of unfaithful
First recorded in 1350-1400, unfaithful is from the Middle English word unfeithful. See un-1, faithful
Related forms
unfaithfully, adverb
unfaithfulness, noun
1. untrustworthy, deceitful, treacherous, recreant. 3. imprecise, untrue. Unabridged
Based on the Random House Dictionary, © Random House, Inc. 2018.
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Examples from the Web for unfaithfulness
Historical Examples
  • Philip was disgusted with her unfaithfulness to his friend, and that was the reason of his absence.

    The Manxman Hall Caine
  • It was not Audrey's unfaithfulness that had hurt him so much as her untruthfulness.

    Audrey Craven May Sinclair
  • The system works well, for unfaithfulness is said to be unknown.

    Ireland as It Is Robert John Buckley (AKA R.J.B.)
  • For three years my husband disgusted me with his unfaithfulness.

    Possessed Cleveland Moffett
  • unfaithfulness and negligence are condemned and punished in both.

    Jesus the Christ James Edward Talmage
  • May hung her head like one accused of gross unfaithfulness, with some show of reason.

    A Houseful of Girls Sarah Tytler
  • unfaithfulness in the keeping of an appointment is an act of clear dishonesty.

    How to Succeed Orison Swett Marden
  • And she gilds her unfaithfulness, forsooth, with the name of divine charity!

    In Convent Walls Emily Sarah Holt
  • He discovered her unfaithfulness months before he disappeared.

    The Art of Disappearing John Talbot Smith
  • You are only giving this as an excuse for your own unfaithfulness.

    Usury Calvin Elliott
British Dictionary definitions for unfaithfulness


not true to a promise, vow, etc
not true to a wife, husband, lover, etc, esp in having sexual intercourse with someone else
inaccurate; inexact; unreliable; untrustworthy: unfaithful copy
(obsolete) not having religious faith; infidel
(obsolete) not upright; dishonest
Derived Forms
unfaithfully, adverb
unfaithfulness, noun
Collins English Dictionary - Complete & Unabridged 2012 Digital Edition
© William Collins Sons & Co. Ltd. 1979, 1986 © HarperCollins
Publishers 1998, 2000, 2003, 2005, 2006, 2007, 2009, 2012
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Word Origin and History for unfaithfulness



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

Online Etymology Dictionary, © 2010 Douglas Harper
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