A tannery is the building or factory where animal skins are turned into leather. Inside, hides are cleaned, soaked in pits or huge drums of chemicals, stretched, and dried. Tanneries are famous for two things: the smell, which is strong and unpleasant enough that towns have always put them at the edge of the settlement or by a river; and the water they dirty, since the chemicals used are hard on the environment. Modern tanneries are cleaner than old ones, but the reputation stays. You will meet this word in travel writing (the open-air tanneries of Fez in Morocco are a famous sight, with their rows of coloured stone pits), in history lessons, in factory and business talk about where leather goods come from, and increasingly in news about pollution and workers' health. The word feels neutral and factual on its own — the bad feeling comes from what people know about the process, not from the word itself.