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

Another ad accuses Paxton of infidelity. —Fort Worth Star-Telegram, 28 Feb. 2026

The other traces a friendship between two middle-aged, male coworkers, both of whom are exploring infidelity—one by having an affair with the other’s wife. —Judy Berman, Time, 26 Feb. 2026

Gunn went on to say that the relationship, which spanned from the mid-'70s to the early '80s, had been punctuated by infidelity. —Anna Kaufman, USA Today, 26 Feb. 2026

Their royal union was complicated by infidelity and intense media scrutiny. —Bailey Bujnosek, InStyle, 25 Feb. 2026

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