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 husband, wife, or partner

b

: unfaithfulness to a moral obligation : disloyalty

2

: lack of belief in a religion

Synonyms

• 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

What follows is a hilarious account of infatuation and infidelity from the point of view of Roberta, a graduate student who has it bad for Simone, her utterly chic — and married — writing professor. —Jasmine Vojdani, Vulture, 1 Aug. 2025

One of the major causes of broken trust between partners is infidelity, but breaches of trust can happen for many other reasons. —Mark Travers, Forbes.com, 31 July 2025

After a tumultuous few years of romance, infidelity, breakups and lawsuits, Fleetwood Mac has been largely inactive for decades, though many of its rotating roster of members have had robust solo careers. —Rachel Treisman, NPR, 29 July 2025

Artists have also used their works to explore themes of culpability and punishment, and to demonstrate the consequences of infidelity for the families of the adulterers. —Smithsonian Magazine, 29 July 2025

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