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 formsun·faith·ful·ly, adverbun·faith·ful·ness, noun

Synonyms for unfaithful

Dictionary.com Unabridged Based on the Random House Unabridged Dictionary, © Random House, Inc. 2019

Examples from the Web for unfaithfulness

Historical Examples of unfaithfulness

  • 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.


    Cleveland Moffett

  • Unfaithfulness and negligence are condemned and punished in both.

    Jesus the Christ

    James Edward Talmage

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; untrustworthyunfaithful copy
obsolete not having religious faith; infidel
obsolete not upright; dishonest
Derived Formsunfaithfully, adverbunfaithfulness, 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

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