unfaithful

1 of 2

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

unfaithfulness

2 of 2

noun

un·​faithfulness

"+

: the quality or state of being unfaithful

Synonyms of unfaithful

Adjective

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

Examples of unfaithful in a Sentence

Adjective

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

Recent Examples on the Web

Adjective

Huang acknowledged being unfaithful to his wife and apologized to his family and the company. — Hollie Silverman, MSNBC Newsweek, 10 Nov. 2026

According to Nvidia, Huang sent an email to his employees on Sunday, acknowledging the relationship, and apologizing for being unfaithful to his wife. — Rebecca Hersher, NPR, 9 Nov. 2026

After Huang on Sunday acknowledged being unfaithful to his wife, Nvidia’s board announced an investigation into reports that he had been targeted by a foreign intelligence effort. — Sebastian Herrera, Fortune, 9 Nov. 2026

The pair broke up in February 2007 after Russell was unfaithful. — Jake Kanter, Deadline, 29 Oct. 2026

Word History

Etymology

Noun

Middle English unfeithfulnesse, from unfeithful + -nesse -ness

First Known Use

Adjective

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