This word is acceptable for play in the US & UK dictionaries that are being used in the following games:

• Lexulous
• Wordscraper
• Wordosaur

n. Unfaithfulness to a sexual partner, especially a spouse.

n. An act of sexual unfaithfulness.

n. Lack of fidelity or loyalty.

n. Lack of religious belief.

n. Unfaithfulness in marriage: practice or instance of having a sexual or romantic affair with someone other than one's spouse, without the consent of the spouse.

n. Unfaithfulness in some other moral obligation.

n. Lack of religious belief.

n. Lack of faith or belief in some religious system; especially, a lack of faith in, or disbelief of, the inspiration of the Scriptures, of the divine origin of Christianity.

n. Unfaithfulness to the marriage vow or contract; violation of the marriage covenant by adultery.

n. Breach of trust; unfaithfulness to a charge, or to moral obligation; treachery; deceit.

n. Lack of faith or belief; unbelief; disbelief: with reference to the essential tenets of any religion.

n. Specifically Disbelief in revealed religion; rejection of the doctrine of inspiration of the Scriptures or of the divine origin of Christianity; or, yet more broadly, disbelief in all forms of religious faith.

n. Breach of trust; unfaithfulness to a charge or an obligation; dishonesty; disloyalty; deceit: as, the infidelity of a friend or a servant.

n. Specifically Unfaithfulness to the marriage-vows; adultery.

n. the quality of being unfaithful

"It's ironic because Sarah's infidelity is the reason the couple find themselves on the beach in the first place."

quality   

falseness    faithlessness    fickleness    inconstancy    disloyalty   

treachery    deceit    heathenism    disbelief    adultery   

immorality    dishonesty    impiety    treachery    heresy    atheism    disobedience    ingratitude    disloyalty    apostasy