I was recently asked why cat is spelled with a c and kitten is spelled with a k. I immediately assumed that cat was Italic and kitten was Germanic, as we would commonly see with these c/k pairs. However, this appears to be a rare exception! Cat comes from Old English catt, which is thought to be from the Proto-Germanic root kattuz, with the same meaning. Kitten, meanwhile, was borrowed in the late fourteenth century from Old French chitoun, a diminutive of chat, their word for "cat". Both chat and kattuz derive from the Latin word cattus, and the best I can guess for the spelling shifts is that cat was changed to look more like the original Latin while kitten was influenced by all the other English words starting with k. Finally, the etymology of cattus is unknown, but similar words crop up from Proto-Uralic to Afro-Asiatic because the animal was traded a lot, so it's muddled and hard to find out more.
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.