Cretin is a word used today as "idiot", but cretinism also refers to people with the medical condition of hypothyroidism, caused by iodine deficiency. This was the earlier definition. In the Middle Ages, people who lived in the Alps tended to be low in iodine. Thus, cretins were born, named crestin in the Franco-Italian region. The word crestin, surprisingly, came from Vulgar Latin christianus, which meant "Christian"! This was for a very inclusive and nice reason: in a surprising show of tolerance, people realized that, despite looking different, cretins were good humans too, and since good humans are Christians, why not label them as such? Christianus traces to Christus, the name for Jesus, and you can get the etymology of that if you look at the post for Christmas. Speeding up to today, a nice, inclusive display by Middle Age denizens of the Alps turned into an insult, just because cretins looked different. Who knows? Perhaps we're getting more barbaric.
Adam Aleksic, a freshman studying linguistics at Harvard University, has been described as the internet's sixth most famous etymologist. He has disturbing interests in words, vexillology, geography, board games, limericks, and law, and he loves writing about himself in the third person.
The Etymology Nerd