The usual infidelity meaning is unfaithfulness to a husband, wife or partner, most often by having a sexual or romantic relationship with someone else. It is the formal word for what people call cheating or having an affair.
The word has a wider and older sense too: a lack of loyalty or faith in general. The sections below cover the infidelity definition used by counselors, its types, the line between infidelity and adultery, the history of the word and some careful ways to use it.
Entry at a glance
Meaning
Unfaithfulness to a partner; more widely, disloyaltyPart of speech
Noun (countable and uncountable: infidelity, infidelities)Pronunciation
in-fi-DEL-i-teeRelated forms
unfaithful (adjective); infidel (a different word today)Origin
Latin infidelitas, faithlessness, from in- (not) + fidelis (faithful)Opposite
Fidelity, faithfulness, loyaltyRegister
Formal or neutral; common in counseling, law and serious writing
Define infidelity: what counts
To define infidelity you have to start with the promise that is broken. In a committed couple, partners usually agree, openly or silently, to be romantically and sexually exclusive. Infidelity is acting against that agreement in secret. What counts can vary from couple to couple, but the main kinds are:
- Sexual or physical infidelity: sexual contact with someone outside the relationship.
- Emotional infidelity: a close, romantic bond with another person that takes the place of the partner, even without physical contact.
- Online infidelity: flirting, sexual messages or secret dating profiles.
Because couples set different rules, counselors often say the key element is secrecy and broken trust, not one exact act.
Infidelity vs adultery and cheating
| Word | Meaning | Tone |
|---|---|---|
| Infidelity | Unfaithfulness in any committed relationship | Formal, neutral |
| Adultery | Sexual relations between a married person and someone who is not their spouse | Legal, religious |
| Cheating | Being unfaithful, broadly | Everyday, informal |
| Affair | A secret romantic or sexual relationship | Neutral |
So all adultery is infidelity, but not all infidelity is adultery: an unmarried couple can face infidelity, and emotional infidelity is not adultery in the legal sense. The opposite idea is fidelity, closely tied to monogamy.
The older meaning: lack of faith
When the word entered English around the early 1400s, it first meant lack of religious faith, or unbelief. Soon after, writers used it for disloyalty to a person, first to a ruler, and by the 16th century to a lover or spouse. That marriage sense is the one most people know today.
You may still see the wider sense in formal writing: infidelity to a cause, infidelity to the original text (a translation that strays from its source). The related word infidel, meaning an unbeliever, is now seen as offensive in most contexts and has drifted apart in meaning.
Infidelity meaning in sentences
- The couple went to counseling after his infidelity came to light.
- She forgave one infidelity but said she would not survive a second.
- The novel follows a family that hides a parent's infidelity for years.
- Many therapists treat emotional infidelity as seriously as a physical affair.
- Critics accused the stage version of infidelity to the original book.
A woman finds months of secret late night messages between her husband and a coworker. Nothing physical happened, he says. She still calls it infidelity, because the closeness and the secrecy broke the trust they had agreed on.
Infidelity and the law
In everyday life infidelity is a personal matter, but in some places it has legal effects. Adultery can be grounds for divorce in many legal systems, including in India and in some US states. India no longer treats adultery as a crime, and while a few US states still have old adultery laws on the books, they are rarely enforced. In some countries adultery remains a criminal offense.
Using the word with care
The meaning of infidelity carries real pain for many readers, so treat the word seriously. Use it in formal or factual writing, and prefer plain talk such as cheating or an affair in casual speech. Common pairings include marital infidelity, accused of infidelity, suspected infidelity and recover from infidelity. The plural, infidelities, refers to separate affairs or acts.
You can explore more relationship words, such as spouse and intimate, alongside dozens of others under people and feelings.
Frequently asked questions
What does infidelity mean for a couple?
For a couple, it is one partner being unfaithful to the other, usually by having a secret romantic or sexual relationship with someone else. It breaks the trust and exclusivity the couple agreed on.
Is emotional infidelity real infidelity?
Many counselors and couples say yes, because it involves secrecy and a romantic bond outside the relationship. Others draw the line at physical contact. It depends on what the couple agreed.
What is the difference between infidelity and adultery?
Adultery is a narrower, often legal term for sex between a married person and someone other than their spouse. Infidelity is broader and covers any unfaithfulness in a committed relationship.
What is the opposite of infidelity?
The opposite is fidelity, meaning faithfulness and loyalty. In relationships, fidelity means staying true to the promise of exclusivity.
Is infidelity a crime?
In most of the world it is not a crime, though it can affect divorce cases. A few countries still punish adultery under criminal law. Laws vary, so local rules matter.
Can infidelity mean something other than cheating?
Yes. In formal writing it can mean disloyalty to a cause, a belief or an original text. Its oldest English sense was lack of religious faith.