Rusts are defined as a reddish-brown coating formed on iron or steel by the oxidation of the metal. There are several synonyms for rusts that can be used depending on the context. Corrosion is a term that is often used to describe rusts, especially in the context of metal surfaces. Oxidation is another synonym that refers to the process of rust formation on metal surfaces. Other words that can be used as synonyms for rusts include decay, deterioration, erosion, and wear. These words are often used to describe the process of rust formation and the damage that it can cause to metal surfaces.