Zlatoust (zlətəōstˈ) [key], city (1989 pop. 208,000), E European Russia, on the Ai River in the S Urals. It is a rail terminus and an old metallurgical center. Besides steel mills, the city has metal-engraving works and factories that manufacture farm machinery, instruments, precision castings, and clocks. Zlatoust was founded in 1754 as one of Russia's first iron industry settlements, and was noted for its swords.