Rust

rust (chel'ah; brosis): Strictly speaking rust is the red oxide of iron formed by the corrosion of that metal, but by extension it has come to mean corrosion produced on any metal. Chel'ah is translated "rust" in Eze 24:11-12. This rendering is probably based on Eze 24:11. Copper caldrons are still used in Bible lands. Such vessels must be constantly watched when on the fire to guard against the possibility of their becoming dry. If this should happen the contents, whatever they may be, and the vessel itself will be injured. The copper of the caldron oxidizes and scales off in black or brownish scales, or rust. ios, was used in Greek to denote the corroding of metals. In Jas 5:3 occurs, "Your gold and your silver are rusted; and their rust .... shall eat your flesh as fire." The writers must have had in mind the actions of chemicals upon these metals which formed some such compound as the caustic silver nitrate.

⇒See the definition of rust in the KJV Dictionary

Brosis, literally, "eating," which occurs in Mt 6:19-20, may refer to the diseases which attack such vegetation as wheat, grapes, cucumbers, etc. In no country is the saying "where moth and rust consume" (Mt 6:19) more true than in Syria. Any metal subject to corrosion seems to rust faster in that country than anywhere else. There are also many rusting fungi which the people have not learned to destroy and which do much damage to the crops.