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

Munson was once married but has been divorced since 2003, citing infidelity as the reason for the split, Bustle reported. —Haadiza Ogwude, Cincinnati Enquirer, 13 Nov. 2025

The couple’s public reckoning with infidelity, emotional abuse allegations and communication struggles was central to the third season. —Jenni Fink, MSNBC Newsweek, 13 Nov. 2025

Kate vehemently denied the infidelity claims at the time. —Caroline Blair, PEOPLE, 13 Nov. 2025

As their once-passionate love life begins to deteriorate, so too does Grace's mental health, leading to explosive fights, violence, and infidelity. —Mike Miller, Entertainment Weekly, 7 Nov. 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