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

In May of this year, Romanucci said, Rivera ended the relationship because of Baker's infidelity. —Darius Johnson, CBS News, 11 Dec. 2025

Her subsequent attempts to uncover some sign of infidelity — or at least a scrap of emotional cheating to justify her own — make everyone so uncomfortable that Dylan eventually just calls it and tells everyone to leave. —Caroline Framke, Vulture, 8 Dec. 2025

Even with dating apps, hookup sites and social media platforms offering more access to potential partners than ever before, many millennials appear to be opting out of infidelity altogether. —Melissa Fleur Afshar, MSNBC Newsweek, 6 Dec. 2025

Her amour fou with lothario bartender Jax Taylor set the tone for a soap whose throughline was infidelity, with the women repeatedly sleuthing out their boyfriends’ indiscretions as the men tried to cover for each other. —Judy Berman, Time, 4 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