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

Vajiralongkorn divorced their mother in 1996 after accusing her of being unfaithful, stripping her and their sons of their titles and forbidding their return to Thailand. —Charlie Campbell, Time, 26 June 2025

People who worked on the nighttime emergency schedule were almost 18 times more likely to be unfaithful to their partners than those who worked part-time. —Mark Travers, Forbes.com, 26 June 2025

Indeed, to rule otherwise would be unfaithful to the judgment and vision of the Founding Fathers! —Sonam Sheth, MSNBC Newsweek, 2 June 2025

But understanding what drives a person to be unfaithful can offer clarity, closure, and even a starting point for healing. —Jenna Ryu, SELF, 11 June 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