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 unfaithful

Contemporary Examples of unfaithful

Historical Examples of unfaithful

  • While men are often unfaithful to their covenant, God never is.

  • He would be as unfaithful to you as he has been to his trust in the bank.


    W. A. Fraser

  • It is ten times better for a woman to marry an unfaithful than a jealous husband.

  • It is lawful for the body to have its desires and its loves, but not to be promiscuous and unfaithful.

    The Golden Fountain

    Lilian Staveley

  • He wondered if it was true that there had been love between these two, and she had been unfaithful.

    The Treasure Trail

    Marah Ellis Ryan

British Dictionary definitions for unfaithful



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 unfaithful

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