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

Defense attorney Emily Smith argued the prosecution’s case lacked key evidence, including the murder weapon, and had little to stand on aside from his infidelity. — Nicki Brown, CNN Money, 29 Sep. 2026

By the end of Volume I, the court romance has devolved into a series of infidelities, both personal and political, which cause the corruption and destabilization of England’s fledgling democracy. — Eileen Hunt, Fortune, 28 Sep. 2026

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

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