Definitions
1.AdjectiveContrary to, forbidden, or not authorized by law, especially criminal law."This is illegal, you know!; Nearly 40 million people live in UK areas with illegal air pollution; Their illegal mining operations in Asia, Africa and elsewhere, are protected by officials and police paid to look the other way – and powerful customers in the construction industry who prefer not to ask too many questions."
2.AdjectiveForbidden by established rules."Moving a pawn backward is an illegal move in chess.; The computer program performed an illegal operation and was terminated."
3.AdjectiveTotally fictitious, and often issued on behalf of a non-existent territory or country.
4.AdjectiveBeing or doing something illegally."illegal immigrant; illegal logger; illegal pilot"
5.AdjectiveBeing an illegal immigrant; residing in a country illegally. (Can we add an example for this sense?)
6.NounAn illegal act or technique.
7.NounContraband, esp. illegal substances such as drugs.
8.NounAn illegal immigrant.
9.NounA spy operating abroad illegally and under non-official cover, without visible ties to his or her country’s authorities.