Why does kitten sound different from cat? To be sure, there is a deal of similarity between the two words, but the similarities are deceptive. Cat comes from Old English catt, from Proto-Germanic *kattuz. Kattuz gives us a number of Germanic words for cat: Old Frisian katte, Old Norse köttr, Dutch kat, Old High Germanic kazza, and German Katze to name a few. We get our first mention of a 'cat' in the English language around 863 CE, found in a Latin-to-English lexicon currently housed in Corpus Christi College, University of Oxford, by an anonymous author. It simply reads:

Fellus (felis), catte.

So cat comes from kattuz, but what about kitten? Kitten comes from the Anglo-French version of Old French chitoun (the Anglo-French languages like Norman gave 'ch' a hard /k/, a vestige from the Latin years, that's why 'castle' doesn't sound like french chateaux). Chitoun comes from Old French chat "cat." We see our first mention of a kitten in Langland's The Vision of William Concerning Piers Plowman, a classic line from 1377 CE:

Þere þe catte is a kitoun þe courte is ful elyng.

Which translated would be...

There the cat is a kitten the court is ummm... something.

Now, where does chat and kattuz come from? Both of them come from Late Latin cattus! It turns out that nearly all European languages have borrowed form either Late Latin cattus or the earlier Latin catta. That's why we have so many similar words in our tongues of Europe. Catta comes from Byzantine dialects of Greek katta. The original Latin word, feles, was replaced by katta around 350 CE.

Katta likely comes from an Afro-Asiatic language -- but we aren't sure which one. There are a number of good candidates...

• Qitt in Arabic
• Kadis in Nubian
• Kadiska in Berber

The phrase "Cat's meow," indicating something cool, is part of a 1920s fad in America in which teens would use an animal and then mark a part of their anatomy. Another classic example is the "Bee's knees." Prior to this 1920s fad, the bee's knees meant something petty or trivial, first used in 1797.