unfaithful

Unfaithful is an adjective that describes a person who is not faithful to someone or something to which they owe loyalty or trust. In everyday usage, it most often refers to romantic or sexual relationships, where one partner engages in sexual or romantic activity with someone else without the other partner's consent or knowledge. The term can also describe betrayal of trust in other relationships, such as friendships, families, or institutions.

Etymology: The word combines the prefix un- meaning 'not' with faithful, with faithful rooted in historical notions of trust.

In relationships, infidelity means violation of the assumed monogamy or trust in a partnership. It can be sexual, emotional, or both. Definitions vary across cultures and relationships; some couples agree to open or nonmonogamous arrangements.

Legal and social aspects: In some legal systems, adultery has historically been grounds for divorce or penalties, but in many places it is no longer criminal and is considered a private matter reflected in civil outcomes such as divorce, alimony, or child custody; fault-based divorce exists in some jurisdictions but is less common.

In culture: The concept features in literature, film, journalism as a means to explore trust, betrayal, consequences, and the complexities of relationships.