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.
Hello! I'm Adam Aleksic. This year, I graduated from Harvard University with a degree in Government and Linguistics. There, I co-founded the Harvard Undergraduate Linguistics Society and wrote a thesis on Serbo-Croatian language policy, magna cum laude. In addition to etymology, I also really enjoy philosophy, trivia, vexillology, geography, board games, conlanging, art history, and law.