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

The album details alleged infidelity by a partner, assumed to be Harbour. —Thomas Smith, Billboard, 30 Oct. 2025

Directed by Kim Ki-young, the film is a cautionary tale about the dangers of infidelity, following a couple that hires a maid to help around the house while the wife is pregnant, only to have the young woman (Lee Eun-shim) destroy the family from the inside out. —Katie Rife, Entertainment Weekly, 28 Oct. 2025

Lily Allen releases her first album in seven years, a shocking album about infidelity in an open relationship. —Taijuan Moorman, USA Today, 27 Oct. 2025

There’s something very reminiscent of Dorothy’s audience with the great and powerful Oz about Elsbeth addressing Raquel without seeing her, and something similarly Oz-like about Raquel herself once she’s confronted with proof of Johnny’s infidelity, too. —Sophie Brookover, Vulture, 24 Oct. 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