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

• disloyal
• faithless
• false
• fickle
• inconstant
• perfidious
• recreant
• traitorous
• treacherous
• untrue

Examples of unfaithful in a Sentence

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

Recent Examples on the Web

The New Yorker story alleged that Willingham had a reputation for drinking too much, being unfaithful and physically abusing Stacy. —Emily Blackwood, People.com, 27 Feb. 2025

Medieval scholars – all men – defined women’s temperament in negative terms: Women were libidinous, frivolous, unfaithful, capricious, unpredictable and easily tempted. —Joelle Rollo-Koster, The Conversation, 25 Feb. 2025

Just days before True's birth, Kardashian learned that Thompson had allegedly been unfaithful. —Jacqueline Weiss, People.com, 21 Feb. 2025

Besides being unsightly, Hephaestus was lame and also had the misfortune of an unfaithful wife. —Cody Cottier, Discover Magazine, 20 Jan. 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