rust (v.) Look up rust at Dictionary.com
early 13c., from rust (n.). Transitive sense "cause to rust" is from 1590s. Related: Rusted; rusting.
rust (n.) Look up rust at Dictionary.com
"red oxide of iron," Old English rust "rust; moral canker," related to rudu "redness," from Proto-Germanic *rusta- (cognates: Frisian rust, Old High German and German rost, Middle Dutch ro(e)st), from PIE *reudh-s-to- (cognates: Lithuanian rustas "brownish," rudeti "to rust;" Latin robigo, Old Church Slavonic ruzda "rust"), from root *reudh- "red" (see red (adj.1)).

As a plant disease, attested from mid-14c. Rust Belt "decayed urban industrial areas of mid-central U.S." (1984) was popularized, if not coined, by Walter Mondale's presidential campaign.