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

Many commenters highlight fears of infidelity, health risks, and the belief that a bisexual man might eventually prefer men, leading to heartbreak. — Razzan Nakhlawi, Washington Post, 10 Oct. 2026

But their relationship cracked amid Hill’s infidelity and a lack of trust, Vaccaro testified. — Milena Malaver, Miami Herald, 7 Oct. 2026

Sure, that sounds ridiculous for a season about rape, infidelity, mass murder, suicide, and society’s ruthless commodification of those very things. — Alison Foreman, IndieWire, 6 Oct. 2026

The 82-year-old actor writes candidly about infidelity, addiction, his son’s imprisonment and his battle with oral cancer, while reflecting on the costs of a life in show business and his love for California. — Maddie Connors, Los Angeles Times, 5 Oct. 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