Illegal (adjective)

1. 1. not allowed by law; prohibited.
2. 2. not authorized by the official rules of a game or sport.

Origin:

Early 17th century: from latin illegalis, from in- "not" + legalis (see legal).

Examples:

1. It is illegal to drive without a seatbelt.
2. This practice is illegal.
3. The company was found guilty of illegal business practices.
4. This drugs are illegal.
5. It is illegal to sell alcohol to minors.