Watchmaking and precision mechanics

The seventeenth entry is o turbilhão, and English owns the word twice over without noticing it. In ordinary Portuguese a turbilhão is a whirlwind, the swirl of dust at a street corner or of water at a weir, and the watchmaking sense is a borrowing back from French, where tourbillon names exactly the same weather. Under all of it sits the Latin turbo, turbinis, the spinning top and the whirlwind, beside the verb turbare, to stir into disorder. From the noun English has « turbine », the wheel a moving fluid spins; from the verb it has « disturb » and « perturb », and, through Old French, « trouble », which is the same stirring applied to a mind rather than to water. So a reader meeting this entry already holds the picture the name is built on: something turning about itself. That is also the mechanism. The cage carrying the balance wheel is made to rotate, so that what one position gets wrong the next one gets wrong in the opposite direction, and the name records the turning rather than the purpose. Keep « tourbillon » in English and leave « whirlwind » to the forecast.