When Cheerios were invented in Minnesota in 1941, they were actually called CheeriOats as a variation of the word "cheery" and a reference to how it was made out of the grain. However, rival company Quaker Oats sued, saying that using the word "oats" was copyright infringement, so General Mills, Cheerios' parent company, changed it to an "o", which worked pretty well anyway, considering that the cereal is o-shaped and "cheerio" can also be an interjection meaning "goodbye". That exclamation emerged in the early twentieth century from the earlier version cheero, which was simply used to wish someone cheer. The word cheer, in turn, actually used to mean "expression", and comes from the Late Latin word carus, meaning "face" (ultimately from PIE ker, "horn").
Hello! I'm Adam Aleksic, a senior studying government and linguistics at Harvard University, where I co-founded the Harvard Undergraduate Linguistics Society. In addition to etymology, I also really enjoy trivia, politics, vexillology, geography, board games, conlanging, art history, and law.