The word bidet has had a fascinating history. When it was borrowed into English in the early seventeenth century, it referred to a specific breed of small horse and we got the modern definition through the notion that people have to straddle a bidet in a similar way that they straddle a small horse. We got it from French, since the horse, now extinct, was native to northwestern France, and its name comes from the verb for "trot", bider. That has an unknown etymology; Celtic origins were proposed by some linguists, but those seem to have been debunked, and there's also an unconfirmed theory that bider comes from Middle French rabider, "to go quickly". Apparently, in the sixteenth century, bidet could also refer to a type of small dagger, but I can't find any research into how that happened or whether that's related.
Hello! I'm Adam Aleksic, a sophomore studying linguistics and government at Harvard University, where I founded the Harvard Undergraduate Linguistics Society. I also have disturbing interests in politics, vexillology, geography, board games, conlanging, and law.