The story goes that the name originated during the 1846-48 Mexican-American War. Supposedly, Yankee soldiers were fond of singing a song, based on a Robert Burns poem [Scottish national poet/songwriter], which was popular at the time, the refrain of which went "Green grow the rushes, O." (Alternate versions of the tale give it as "Green grow the lilacs.") The Mexicans, probably as tired of hearing the song as you are of the latest Top-40 hit, began calling the Americans "green grows," which eventually became gringos.
I soldati yenkee amavano cantare una canzone, basata su una poesia di Robert Burns [poeta/canzoniere nazionale scozzese], molto popolare in quel periodo, il cui ritornello faceva "Green grow the rushes, O." (Una versione alternativa della storia sarebbe "Green grow the lilacs"). I Messicani, probabilmente stanchi di sentire questa canzone, come voi ora di un successo delle ultime Top-40, iniziarono a chiamare gli Americani "green grows", che poi divenne gringos.