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

Struggling to retain custody of her three-year-old son after leaving her unfaithful husband, Naru is convinced that no good men exist in her country — until a career opportunity offered by Qodrat, the station’s most influential journalist, forces her to reconsider. —Elsa Keslassy, Variety, 18 Jan. 2026

Noth has not been formally charged or sued in connection with the allegations, and claimed that his only offense was being unfaithful to his wife, Tara Wilson. —Sydney Bucksbaum, Entertainment Weekly, 14 Jan. 2026

Turns out, my husband has been suspicious of my evenings away and is now accusing me of being unfaithful. —Harriette Cole, Mercury News, 29 Dec. 2025

Their love was no longer a secret, or a lie, or unfaithful. —Penn Badgley, Vulture, 1 Dec. 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