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

Both men had allegedly been unfaithful. —Madison E. Goldberg, PEOPLE, 7 Oct. 2025

There’s a sociological connection between some things that anti-liberals say and some things that certain liberals say, and that’s because certain liberals were unfaithful to their liberalism. —Isaac Chotiner, New Yorker, 23 Sep. 2025

However, their relationship deteriorated once Paul found proof that Mortensen was unfaithful early in their relationship and had lied to her for years. —Monica Mercuri, Forbes.com, 10 Sep. 2025

Ultimately, the romance ended after Christine admitted to being unfaithful. —Allison Degrushe Published, EW.com, 15 Aug. 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