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

And so infidelity has emerged as one of this show’s defining themes, too. —Judy Berman, Time, 4 Dec. 2025

That mourning, displacing infidelity, has been restored to its central place in Shakespeare’s inspiration is perhaps a good thing, though not necessarily a true one. —James Shapiro, The Atlantic, 1 Dec. 2025

This is a comedy about infidelity and divorce, but the unpredictable way its scenes unfold — a sudden car crash here, an extended beatdown there — reflect the totally unmoored nature of these characters’ lives. —Alison Willmore, Vulture, 1 Dec. 2025

Many have speculated that Kubrick was not finished with the film — an erotic mystery starring a very real couple as a fictional one torn apart by jealousy and infidelity over one night in New York City — or even pleased with the version sent to brass. —Ryan Lattanzio, IndieWire, 24 Nov. 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