The term "rusty nail" generally refers to a nail that has been exposed to rust, which is a corrosive process that occurs when iron or metal is exposed to water or air. However, there are several other synonyms that can be used to describe the same object. These include "corroded nail", "decayed nail", "oxidized nail", "weathered nail", and "old nail". Each of these phrases conveys the same meaning as "rusty nail", describing a metal nail that has undergone a process of deterioration. These synonyms can be used interchangeably in order to add variety and interest to your writing.