foul

Foul is a term with multiple related meanings in English, used as an adjective, noun, and verb. As an adjective, it describes something dirty, contaminated, or offensive to the senses or morals—such as a foul odor, foul water, or foul language. It can also refer to morally wrong or deceitful behavior, as in foul play. As a verb, to foul something means to soil, pollute, or spoil it, and in informal use to foul up a process means to disrupt or ruin it. As a noun, foul denotes an infraction or violation, especially in sports, or the act of foul play more generally.

Etymology traces foul to Old English fūl, meaning dirty or filthy, with roots in Proto-Germanic likely related to terms for dirtiness in other Germanic languages. The sense of violation or wrongdoing developed over time, expanding to describe both physical contamination and rule-breaking behavior.

In sports, a foul is a violation of the rules that typically results in a penalty or free possession for the opposing side. The concept appears in many codes, including soccer, basketball, football, rugby, and others, where contact, offside, or dangerous play can constitute a foul. In baseball, a foul ball is a batted ball that lands outside the fair territory, and foul play has historically referred to criminal or deceitful conduct during a game or match.

Beyond sports, foul usage covers language or actions considered morally or socially unacceptable, as well as contaminated substances or environments. The meaning of foul is highly context-dependent, ranging from physical dirt to moral or procedural wrongdoing.