Yours, Etc.: Origins and Uses of 8 Sign-Offs
1947, from Mexican Spanish dialectal pronunciation of Mexicano "Mexican," with loss of initial unaccented syllable [Barnhart]. Said to have been in use among Mexican-Americans from c.1911. Probably influenced by Spanish chico "boy," also used as a nickname. The adjective in English is attested by 1967. Fem. form is Chicana.