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

An attorney retained by Andrew’s family told ABC7 that moments before the killing, Andrew read a diary entry in which his wife described engaging in infidelity. —Clara Harter, Los Angeles Times, 24 Jan. 2026

One of the more memorable moments between the two was the reveal of Cooke's infidelity during the premiere of season 3, which aired in March 2019. —Mekishana Pierre, Entertainment Weekly, 20 Jan. 2026

Kristy alleged infidelity as the reason for the pair’s split, per court records previously obtained by PEOPLE. —Luke Chinman, PEOPLE, 19 Jan. 2026

The Woods brand was badly dinged by his November 2009 car crash and infidelity scandal, but sponsors returned for the comeback story, including his 2019 Masters title. —Kurt Badenhausen, Sportico.com, 30 Dec. 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