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

Wole’s infidelity is an important inciting incident, but this moment of personal reckoning was inevitable. —Cressida Leyshon, New Yorker, 28 Sep. 2025

This type of infidelity can stem from dissatisfaction in the relationship or a desire for something different. —Melina Khan, USA Today, 25 Sep. 2025

Lorenzo must deal with the repercussions of his infidelity and the weight of all the manipulation. —Isabella Wandermurem, Time, 24 Sep. 2025

Meanwhile, Lian and Wenyu wrestle with their own infidelities. —Michael Schaub, Oc Register, 22 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