Creosote is a thick, dark-brown oil with a sharp, burnt smell. People brush it onto wood that has to live outside — fence posts, the heavy beams under train tracks — because it soaks in and stops the wood from rotting. It is not a friendly stuff: you should not get it on your skin or breathe it in if you can help it, and the smell hangs around for a long time. Though actually, the name is older than fence-painting. In the 1830s a German scientist, Baron Reichenbach, built the word from Greek pieces meaning “flesh” and “preserver”, because this kind of oil was used to keep meat from going bad. A desert bush in America was later called the creosote bush only because its leaves smell like the oil — the bush is not the liquid. You will also hear creosote as a verb: to creosote a fence is to paint it with this oil. It is a practical, outdoor word, a little old-fashioned; you meet it in gardening, railways, and old buildings more than in school stories.