gringo
The word originated in Mexico, when the United States of [America] invaded Mexico in order to appropiate half of its territory, back on mid 19th century. Of course this action against "[peace] and freedom" is not in elementary [school] textbooks in USA, but it is in any other serious document about USA history.
American soldiers entered the country through the Gulf of Mexico, taking down the main port of Veracruz and then heading towards Mexico City. The troops were wearing GREEN COATS.
Mexican [people] along the way from Veracruz to Mexico suffered the advance of the enemy and many battles were fought. However, the American army finally reached Mexico City and took the city down in an epic battle still remembered by all the Mexicans: The battle of Chapultepec Castle. This palace, in the [top] of a hill, is the highest point over Mexico City: there was the Mexican flag, so it was a symbolic target.
The headquarters of the Military [College] were in Chapultepec castle too, and when the "green coats" were climbing the hill, a few young cadets refused to leave and decided to defend the castle to [death]. Then, when the battle was helplessly lost, one of the cadets took the Mexican flag, wrapped himself on it and jumped off the cliff were the castle is set, dying in the rocks below, thus avoiding the American army to take the flag. When the American commander saw the corpses of the cadets, he said in amazement "They are only children!". So they became in [death] Los Niños Héroes, the symbol in Mexico of the resistance against invaders: the American army... the green coats.
The war was over and USA claimed half of Mexico's territory... then the green coats went home, having gained possesion of [Texas] and other territories -and their resources- (the same old motif than nowadys, but the speech has changed).
Ever since, the relationtship USA-Mexico has developed into a very complex love-hate relationtship and the [destiny] of both nations is linked together, but back then, a new term was born in popular language: gringo (green coat)
Now, let's make clear that the term is used nowadays the same as affectionate as pejorative and as none of the above too. As complex as it seems, Mexican [people] can use the word with different intentions but in any case with just [one] meaning: it refers in a common way to USA citizens, who are distinctive not because of the colour of their skin, but because of their culture and behavior (anyone outside USA knows exactly what behavior is it!)
Other derivatives of the word include:
gringa: female for gringo, as substantive.
gringo/gringa: as adjectives.
agringado: something/someone that resembles USA culture or the American way of life.
Gringolandia: U.S.A.
As a final note i must say that the word spread to other countries over Latin [America] (even to Spain) where it is used to refer to foreigners and/or white [people]: but that's just the way some [people] outside Mexico understand the word!
Nevertheless, in Mexico, a "gringo" is just an American citizen. And it implies nothing else.
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Gringo loco!
Crazy American!
Las películas gringas tienen los mejores efectos especiales.
American films have the best special effects.
Las gringas son facilotas.
American girls (springbreakers) are promiscuous.
Esa casa es de estilo agringado.
That [house] has an American-like style (meaning it is a [new] rich tasteless [house])
Los gringos creen que son los policías del mundo.
Americans think they are the [police] of the world.
En Gringolandia pasan todas las desgracias: meteoritos, tormentas [y] ¡hasta Godzilla!
In U.S.A. happens all kind of disfortune: meteores, storms and even Godzilla!
This definition is too long for this mug.