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

Platner is also an unfaithful spouse who mistreats women. — Chris Roemer, Baltimore Sun, 25 June 2026

In Strangers on a Train, Rogers played Guy's unfaithful wife, whom Bruno offers to kill. — Emily Blackwood, PEOPLE, 29 June 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

Starring Yakusho Koji, the film follows a man released on parole after killing his unfaithful wife. — Naman Ramachandran, Variety, 13 May 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