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

The garment, which went on public display Friday at Sotheby’s in London, was worn by Diana on June 29, 1994, the broadcast date of an interview in which the then-Prince Charles acknowledged infidelity. — ABC News, 18 Sep. 2026

Just days later, Bullock and James separated following reports of his infidelity, and Bullock raised Louis as a single mom. — Allison Degrushe, StyleCaster, 15 Sep. 2026

Zvyagintsev’s story, like Chabrol’s, imagines the tragic fallout of a husband discovering his wife’s infidelity. — David Canfield, HollywoodReporter, 14 Sep. 2026

His relationship with his wife (Anna Faris) and kids is disintegrating and a National Enquirer journo keeps threatening to run an exposé of his infidelities. — Jessica Kiang, Variety, 5 Sep. 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