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

• 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

Speculation was particularly concentrated on a rumor that Bryan had been unfaithful to Amaya, which gained traction on social media, and while neither Bryan nor Amaya weighed in on it, Bryan's dad made sure to quell the rumors. —Julia Moore, People.com, 5 Aug. 2025

Cassie Ventura, the case’s star witness and another former girlfriend of Combs, testified Combs was unfaithful to her by dating Gina throughout their 11-year relationship. —Elizabeth Wagmeister, CNN Money, 3 Aug. 2025

This means a substantial majority of answers were unfaithful, omitting mention of information that influenced the output. —ArsTechnica, 10 Apr. 2025

Duggar claims the government used a statement posted to his family's Facebook page and attributed to him claiming Duggar had secretly viewed pornography, led a double-life and had been unfaithful to his wife. —Arkansas Online, 29 July 2025

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