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").

I recently stumbled on a fascinating Twitter thread concerning the etymology of Triscuit​ crackers, which until last year was lost to the annals of history. At first glance, one would assume that it just means "thrice cooked", since the word biscuit translates to "twice cooked". Enter Sage Boggs, a writer for the Tonight Show Starring Jimmy Fallon, who emailed the Nabisco corporation in March 2020 just to confirm that tri- did, in fact, mean "three". After receiving a cryptic message that they didn't know the etymology but it didn't mean "three", Boggs did a little digging and came up with old Triscuit advertisements from the early 1900s touting that the crackers were "baked by electricity". Elec-tri-city. Triscuits are "electric biscuits", and this was eventually confirmed by the company, which sent Boggs a large batch of complimentary crackers as a reward.

The verb exhaust first started showing up in English in the mid-sixteenth century, with pretty much the same definition as today. It's borrowed from Latin exhaustus, which is the past principle of the verb exhaurire, meaning "to draw off" or "to use up". That's composed of the prefix ex-, meaning "out", and the root haurire, meaning "to draw up" (as in water) or "take out". More figuratively, it could mean "remove", and that's how we got the sense of exhaust being something that's pushed away rather than pulled toward, despite the Romans maybe having a different conceptualization of the word. Finally, haurire comes, through Proto-Italic auzjo, from the Proto-Indo-European reconstruction hews, meaning "east" or "dawn", with the connection being the notion of the sun being drawn upwards.

The word obsequious, meaning "excessively obedient", was borrowed in the late fifteenth century from Latin obsequiem, which pretty much meant the same thing but in a less pejorative sense. That's from the prefix ob-, here meaning "after" (from Proto-Indo-European epi, "against"), and the verb sequi, which meant "to follow" in Latin. This is the same root as the one we see in non sequitur (something that does not follow), consecutive (something that follows together), suitor (one who follows another), sequel (something that follows), and many more similar words. Finally, etymologists reconstruct sequi to the Proto-Indo-European root sekw, which also just meant "to follow". Since its introduction into the English language, obsequious​ peaked in usage in 1779 and has been on the decline since.

In 1651, Thomas Hobbes became the first person to use the word leviathan in the context of political entities, but it was in use since 1606 with the meaning "person of formidable wealth or influence". This sense emerged from an earlier reference to the gigantic sea serpent that shows up in several books of the Bible - the leviathan person, like the creature, possessed great power. The word, through Latin, comes from Hebrew livyathan, which could be used for several large animals, including dragons, serpents, and various sea monsters. That has an uncertain etymology, but the main theory that's been proposed is that it traces to the Proto-Semitic root l-w-h, meaning "twist", with the definition changing based on the notion of a serpent coiling itself. This would make it related to the Hebrew word for "wreath", liwyah, and the Arabic word for "bend", lawa​.

When the word turnpike was first used in the English language in 1420 CE, it referred to a spiked barrier set up across a road to prevent attacks on horseback. In the seventeenth century, this sense got extended to a kind of barrier that was raised on roads until a toll was paid, and eventually to any kind of expressway with a toll. The word, simply enough, comes from turn and pike (the kind of spiked weapon), because the original turnpikes were often constructed at turns and out of pikes. Turn, through Old French torner, comes from Latin tornus, meaning "lathe", and that's from Ancient Greek tornos, with the same definition. Pike, which is also the source of the fish name due to a perceived physical resemblance, comes from Old French pic, meaning "sharp point", and that has several proposed etymologies.