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

In the movie, the Bullmers’ relationship is still fraught, but the issues are based more in money than infidelity, and Anne (Lisa Loven Kongsli) is far more of a presence. —Roxana Hadadi, Vulture, 10 Oct. 2025

The two shared a tumultuous partnership that included allegations of infidelity, and divorced in 1967. —Raven Brunner, PEOPLE, 8 Oct. 2025

From Sandra Bullock facing heartbreak when her then-husband Jesse James admitted to infidelity, to Reese Witherspoon moving on with a summer romance after her divorce, here's a look at Kidman’s Hollywood inner circle and their high-profile romances that have been in the spotlight. —Stephanie Giang-Paunon, FOXNews.com, 4 Oct. 2025

Wole’s infidelity is an important inciting incident, but this moment of personal reckoning was inevitable. —Cressida Leyshon, New Yorker, 28 Sep. 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