Though everyone has a pet theory about the origins of the word gringo, its etymology is unclear. The most popular explanation is that Yankee soldiers sang the song “Green Grow the Lilacs” during the Mexican-American War, prompting Mexican soldiers to shout “Green Go” in response. However, the term was in use before the 19th century, making this explanation unlikely. Other theories suggest that the word derives from griego, the Spanish word for Greek (and possibly a term applicable to any foreigner speaking a foreign tongue).
Finally, is the term derogatory? There is a persistent rumor that the term gringo is pejorative, and, in some cases, it is. When used in a sentence such as, “fast food is a gringo invention,” the word can imply a certain low grade from the United States, which is generally disrespected in Mexico. However, in the great majority of cases, the word gringo is simply a descriptor, much easier on the tongue than the cumbersome official term estadounidense (U.S. citizen). As you’ll quickly learn, many expatriates freely refer to themselves as gringos, and Mexicans use it without any implied offense. As an alternate to gringo, the word gabacho also refers to people or things from the United States. Though it is used less frequently, it is a synonymous with gringo and can be used interchangeably. For this word, we have a stronger sense of its origins, since the Spanish used gabacho to describe the French.
Finally, the popular moniker güero is a much more general term, though it’s commonly used to describe foreigners. Güero refers to any person with fair hair and skin. There is no political connotation to the term güero, and Mexicans will even refer to fair-haired compatriots as güeros.
Excerpted from the Second Edition of Moon Living Abroad in Mexico.