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

• disloyalty
• faithlessness
• falseness
• falsity
• inconstancy
• perfidiousness
• perfidy
• unfaithfulness

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 entrepreneur and wellness coach addressed rumors of infidelity while responding directly to a fan’s accusation on Instagram. —Amber Corrine, VIBE.com, 23 May 2025

Honey is typically in the business of infidelity, taking cases involving suspicious spouses and their philandering partners. —Lovia Gyarkye, HollywoodReporter, 23 May 2025

But just as monogamy’s definition has changed and means different things to different people, the same is true for infidelity. —Myisha Battle, Time, 19 May 2025

At 33, Brian, the Redditor's husband, firmly falls into this bracket, though the level of financial infidelity described in the social media post will take some beating. —Jack Beresford, MSNBC Newsweek, 16 May 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