What does illegal mean?
Illegal means forbidden by law or contrary to legal rules. It is widely used to describe crimes and criminal conduct, but its application can also extend to immigration status, employment, business practices, possession, and activities governed by regulations. In everyday language, the word can simply mean “not allowed,” although its legal and moral associations often make it more emphatic than a neutral phrase such as “prohibited.” The related adverb “illegally” describes an action performed in violation of the law, while “illegality” names the state or condition of being illegal. Because legality depends on the laws and regulations of a particular jurisdiction, describing something as illegal normally implies a public legal prohibition rather than merely a personal or moral objection.
adjectiveForbidden or prohibited by law; not lawful. The term can also describe an activity or status that is contrary to official rules or regulations.
- Prohibited or forbidden by law.
- Contrary to official rules, regulations, or established procedures.
"The company was accused of engaging in illegal environmental practices."
"Investigators found evidence that the business had been operating illegally."
"Parking in that area is illegal, even when the signs are difficult to see."
Illegal is more than “not allowed”: it specifically points to conduct that conflicts with the law.
Reviewed by Deb Chak, Editor. AI-assisted content curated by RJS Tech Solutions LLP.
Where does illegal come from?
The word entered English in the early 17th century from French illégal, which was formed with the Latin negative prefix in- and legalis, meaning “lawful.” The underlying language was Medieval Latin illegalis, meaning “contrary to law.” Its modern relatives include legal, legalize, and legalization, all based on the Latin root associated with law.
Related word forms
How illegal is actually used
The word is common in legal, journalistic, and everyday contexts. It can sound formal or strongly condemnatory, depending on context; “unlawful” may be preferred in formal legal writing when precision is important.
Easily confused with illegal
Both mean contrary to the law, but “unlawful” is the broader and more formal term, while “illegal” is especially common in general and legal usage.
“Illegal” describes conduct or conditions that violate the law, whereas “legal” means permitted by and consistent with it.