Mexican

wiktionary

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From Spanish mexicano, from Nahuatl mēxihcah plural of mēxihcatl(“a Mexica”) + -ano(“ -an”)

etymonline

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Mexican

c. 1600 (n.) "native or inhabitant of Mexico;" by 1640s (adj.) "native of or pertaining to Mexico or its inhabitants," from Mexico + -an. In the old U.S. Southwest it served as a general pejorative or dismissive adjective, much as Dutch did in the northeast: Mexican strawberries "beans;" Mexican standoff "battle that no one wins;" Mexican breakfast "a glass of water and a cigarette," etc.