forbidden by law or statute.
contrary to or forbidden by official rules, regulations, etc.: The referee ruled that it was an illegal forward pass.


Informal: Disparaging and Offensive. illegal alien.

Origin of illegal

From the Medieval Latin word illēgālis, dating back to 1620–30. See il-2, legal
Related formsil·le·gal·ly, adverb
Can be confusedillegal illicit (see synonym study at the current entry)

Synonyms for illegal

Synonym study

1, 2. Illegal, unlawful, illegitimate, illicit, criminal can all describe actions not in accord with law. Illegal refers most specifically to violations of statutes or, in organized athletics, codified rules: an illegal seizure of property; an illegal block ( in football ). Unlawful means not sanctioned by or according to law: an unlawful claim to the inheritance; to take unlawful advantage of the trading situation. Illegitimate means lacking legal or traditional right or rights: an illegitimate child; illegitimate use of privileged knowledge. Illicit, which originally meant simply “not permitted,” now most often applies to matters regulated by law with specific emphasis on the way things are carried out: illicit conversion of property; an illicit attempt to control the market. Criminal most often refers to violation of the statutes of penal as opposed to civil law. All felonies are criminal as are all crimes sometimes punishable by death such as murder, arson, and kidnapping: a criminal act.

Usage note Unabridged Based on the Random House Unabridged Dictionary, © Random House, Inc. 2019

Examples from the Web for illegal

Contemporary Examples of illegal

Historical Examples of illegal

  • With a man of that sort scrupulousness was a misplaced and even an illegal sentiment.

    The Secret Agent

    Joseph Conrad

  • They'll do their best to get him, and if they do there'll be trouble of an illegal nature.

  • After all persuasions had failed, we had tried threats: the thing he purposed to do was illegal.

    Lotus Buds

    Amy Carmichael

  • He had no wish to be discovered there—his entrance had been too irregular, too illegal, for that.

    The Film of Fear

    Arnold Fredericks

  • That is to say, somewhere and at some time there has been a transfer of that property that was illegal.

    Thankful's Inheritance

    Joseph C. Lincoln

British Dictionary definitions for illegal



forbidden by law; unlawful; illicit
unauthorized or prohibited by a code of official or accepted rules


a person who has entered or attempted to enter a country illegally
Derived Formsillegally, adverbillegality, noun
Collins English Dictionary - Complete & Unabridged 2012 Digital Edition © William Collins Sons & Co. Ltd. 1979, 1986 © HarperCollins Publishers 1998, 2000, 2003, 2005, 2006, 2007, 2009, 2012

Word Origin and History for illegal

1620s, from French illégal or directly from Medieval Latin illegalis, from assimilated form of in- "not, opposite of" (see in- (1)) + Latin legalis (see legal). Term illegal immigrant first recorded 1892 in American English (illegal immigration is from 1887).

Online Etymology Dictionary, © 2010 Douglas Harper