infidelity

noun

in·​fi·​del·​i·​ty ˌin-fə-ˈde-lə-tē 

-(ˌ)fī-

plural infidelities

1

a

: the act or fact of having a romantic or sexual relationship with someone other than one's spouse or partner

b

: unfaithfulness to a moral obligation : disloyalty

infidelity to the group's guiding principles

2

: lack of belief in a religion

Synonyms of infidelity

• adultery
• betrayal

Examples of infidelity in a Sentence

She was convinced that her husband was guilty of infidelity.

He has admitted to a number of marital infidelities.

Recent Examples on the Web

The same day Diana wore the gown, her estranged husband admitted to infidelity on national television. — Bailey Bujnosek, InStyle, 9 July 2026

Plots tend to involve women in various types of distress, facing things like murder, stalking, infidelity, illicit love, kidnapping, and storm-chasing serial killers. — Brianna Zigler, Entertainment Weekly, 7 July 2026

Last month, six women interviewed by the Times described concerning behavior by Platner, including excessive drinking, infidelity, and, in one account, physical intimidation. — Allison Gordon, CNN Money, 6 July 2026

Ocasio-Cortez notably sidestepped Platner’s candidacy in Maine even as other progressives defended him from the controversy surrounding his infidelity and old social media posts. — David Sivak, The Washington Examiner, 4 July 2026

Word History

Etymology

Middle English infidelite, borrowed from Middle French infidelité, borrowed from Latin infidēlitāt-, infidēlitās "faithlessness, inconstancy," from infidēlis "unfaithful, disloyal" + -itāt-, -itās -ity — more at infidel entry 2

First Known Use

15th century, in the meaning defined at sense 2

Rhymes for infidelity

• fidelity

Kids Definition

infidelity

noun

in·​fi·​del·​i·​ty ˌin-fə-ˈdel-ət-ē 

-(ˌ)fī-

plural infidelities

1

: lack of faith in a religion

2

: unfaithfulness especially to one's husband or wife