illegal (adj.) Look up illegal at Dictionary.com
1630s, from French illégal (14c.) 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); used in British English in 1940s in reference to the Jewish movement to Palestine.