unfaithful

adjective

un·​faith·​ful ˌən-ˈfāth-fəl 

: not faithful:

a

: not adhering to vows, allegiance, or duty : disloyal

an unfaithful friend

b

: not faithful to marriage vows

suspected her husband of being unfaithful

c

: inaccurate, untrustworthy

an unfaithful copy of a document

unfaithfully

ˌən-ˈfāth-fə-lē 

adverb

unfaithfulness noun

Synonyms of unfaithful

• traitorous
• unreliable
• false
• faithless
• disloyal
• treacherous

Examples of unfaithful in a Sentence

colonists who later proved to be unfaithful to the cause of independence

Recent Examples on the Web

Upon discovering that her abusive husband (Caleb Landry Jones) had been unfaithful, Becky drove off with her parents' car and shot at the door of his mistress' apartment. —Drew MacKie, PEOPLE, 11 Apr. 2026

Their acrimonious split the following April was ushered in by the Love Thy Nader star's accusation that Savchenko was unfaithful. —Ryan Coleman, Entertainment Weekly, 10 Apr. 2026

Moreover, quotas or preferences divorced from character and accomplishments are unfaithful to individual rights and responsibilities and a temptation to tribalism. —Bruce Fein, Baltimore Sun, 5 Mar. 2026

Early images from filming showed outfits which were derided online as cheap-looking—and unfaithful to the late Bessette Kennedy’s real aesthetic. —Bailey Bujnosek, InStyle, 21 Feb. 2026

Word History

First Known Use

15th century, in the meaning defined above

Rhymes for unfaithful

• faithful

Kids Definition

unfaithful

adjective

un·​faith·​ful ˌən-ˈfāth-fəl 

ˈən-

1

: not observing vows, allegiance, or duty : disloyal

an unfaithful friend

2

: not faithful to marriage vows

3

: inaccurate

an unfaithful translation

unfaithfully

-fə-lē 

adverb

unfaithfulness noun