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

The golden calf famously enraged Moses, showing that the Israelites had turned away from God and were unfaithful in Moses’s absence. —Britta Miller, The Washington Examiner, 9 May 2026

Portraits of him as a cheating drunk, who was unfaithful to his first wife, Julia Nye, also surfaced. —Kory Grow, Rolling Stone, 6 May 2026

Speculation immediately followed surrounding what caused their beak-up, including that Keoghan was unfaithful. —Jessica Schladebeck, New York Daily News, 28 Apr. 2026

This story isn't nearly as exciting because an NBA player being unfaithful to his girlfriend sort of just feels like a regular Thursday afternoon. —Amber Harding Outkick, FOXNews.com, 28 Apr. 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