Latin focus meant ‘fireplace’, and in post-classical times it came to be used for ‘fire’ itself – hence French feu, Italian fuoco, Spanish fuego, all meaning ‘fire’, and hence too the English derivatives fuel and fusillade. The first writer known to have used it in its modern sense ‘point of convergence’ was the German astronomer Johannes Kepler, in 1604, but the reason for his choice of word is not clear.