General Antonyms:
* Illegal: This is the most direct opposite of "legal," meaning against the law.
* Unlawful: Similar to "illegal," this word emphasizes that something is not permitted by law.
* Illicit: This word suggests something is forbidden or secretive, often with negative connotations.
Other Possible Antonyms:
* Informal: This refers to something not governed by formal rules or laws.
* Unregulated: This describes something without any official controls or restrictions.
* Extralegal: This refers to something outside the legal system, potentially implying it's not subject to or recognized by law.
The best antonym for "legal" will depend on the specific context and the meaning you want to convey.