illegal vs legal

illegal

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

  • Breaching certain enacted statutes of positive law; not lawful, not legal (cf. immoral, unethical) 

  • Forbidden by established rules. 

  • Being or doing something illegally. 

  • Being an illegal immigrant; residing in a country illegally. 

  • Totally fictitious, and often issued on behalf of a non-existent territory or country. 

noun
  • An illegal immigrant. 

  • Contraband, esp. illegal substances such as drugs. 

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

legal

adj
  • Relating to the law or to lawyers. 

  • Having its basis in the law. 

  • Being allowed or prescribed by law. 

  • Above the age of consent or the legal drinking age. 

  • Following the rules or syntax of a system, such as a game or a programming language. 

  • (of paper or document layouts) Measuring 8½ in × 14 in (215.9 mm × 355.6 mm) (also legal-size). 

noun
  • Paper in sheets 8½ in × 14 in (215.9 mm × 355.6 mm). 

  • The legal department of a company. 

  • Somebody who immigrated lawfully. 

  • A spy who is attached to, and ostensibly employed by, an embassy, military outpost, etc. 

How often have the words illegal and legal occurred in a corpus of books? (source: Google Ngram Viewer )