Origin: 1620–30; < Medieval Latinillēgālis. See il-2, legal
Can be confused: illegal, illicit (see synonym study at the current entry).
Synonyms 1. unlawful; illegitimate; illicit; unlicensed. 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.
1626, from M.L. illegalis, from L. in- "not" (with assimilation of -n- to the following consonant) + legalis (see legal). Term illegal immigrant first recorded 1939 in ref. to Jews entering Palestine without authorization during the British mandate.