Rustiness is a term often used to describe the condition of something that has corroded due to exposure to moisture and air. However, there are other synonyms to this word that can be used to describe the same condition. Some of these synonyms include decrepitude, decay, deterioration, weathering, erosion, and damage. Each of these words conveys a sense of something that has weakened or gradually become worn out over time. While these words can be used interchangeably, they each add a different nuance to the overall meaning of rustiness and help to create a more specific and descriptive picture of the object or material being discussed.