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Infidelity is when someone who is married, or in a couple, has sex with a person who is not their wife, husband, or partner. People sometimes stretch it a little to cover a secret love affair even before sex, but the core is breaking the promise of being only with that partner.
Infidelity infidelity is指的是 when someone who is married, or in a couple已婚或有伴侶的人 has sex with a person who is not their wife, husband, or partner跟不是自己太太、先生，或伴侶的人發生性行為 People人們 sometimes stretch it a little有時候會把定義放寬一點 to cover a secret love affair even before sex包含性行為之前的秘密戀情 but但 the core核心 is breaking the promise of being only with that partner都是打破了只跟這個伴侶在一起的承諾
It is a formal, serious word: newspapers, lawyers, and quiet conversations use it. Everyday talk more often says cheating or an affair.
It它 is a formal, serious word是一個正式、嚴肅的字 newspapers, lawyers, and quiet conversations報紙、律師，和私下的談話 use it會用它 Everyday talk日常對話 more often says比較常說 cheating or an affair cheating（劈腿/出軌）或an affair（外遇）
Though actually, the word sits in the same family as faith and , and long ago it could also mean not being true to a religion. Today, if you hear infidelity with no extra context, people almost always mean cheating in love, not religion.
Though actually不過其實 the word這個字 sits in the same family as faith and infidel跟faith和infidel是同一個字族 and而 long ago很久以前 it它 could also mean not being true to a religion也可以指對宗教不忠 Today現在 if you hear infidelity with no extra context如果你聽到infidelity、沒有其他上下文 people大家 almost always mean cheating in love幾乎都是指感情上的不忠 not religion不是宗教
原始詞典資料3 筆記錄
以下是外部詞典記錄的用法，原文照列，我們還沒有寫成教學內容。上面的說明才是我們自己寫的；有些用法可能上面已經講過了。
infidelitynoun/ˌɪnfɪˈdɛlɪti/
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Unfaithfulness in a marriage or an intimate (sexual or romantic) relationship: practice or instance of having a sexual or romantic affair with someone other than one's spouse, without the consent of the spouse.
- Your friends tell you rumors about your girlfriend's infidelity or you remember being broken up around the time the baby was conceived.
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Unfaithfulness in some other moral obligation.
- It was disastrous that England's infidelity towards Frederick the Great — which no one, not even a German, condemned more strongly than did William Pitt — had to affect one of the most popular heroes of our national history.
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archaicLack of religious belief.
- The means used to this purpose are partly didactical, and partly protreptical; demonstrating the truth of the gospel, and then urging the professors of those truths to be stedfast^([sic]) in the faith, and to beware of infidelity.
- The Churchman remarked that such incidents arose from the growing infidelity, while the Freethinker saw in them a reversion to superstition.
資料來源：英文維基詞典 English Wiktionary（CC BY-SA 4.0）。 原文照列，未經改寫。