Meaning

• An illegal act or technique.

• (plural, as illegals) Contraband, esp. illegal substances such as drugs.

• An illegal immigrant.

• A spy working abroad illegally and undercover, without visible ties to his or her country’s authorities.

Meaning

• Contrary to or forbidden by law, especially criminal law.

  "Nearly 40 million people live in UK areas with illegal air pollution"

• Forbidden by established rules.

  "Moving a pawn backward is an illegal move in chess."

• (of an issue printed for collectors) Totally fictitious, and often issued on behalf of a non-existent territory or country.

• (of a person, sometimes offensive) Being or doing something illegally.

  "illegal immigrant;  illegal logger;  illegal pilot"

• (sometimes offensive) Being an illegal immigrant; residing in a country illegally.