rust 
(rŭst)
(rŭst)n.
1.
a. Any of various powdery or scaly reddish-brown or reddish-yellow hydrated ferric oxides and hydroxides formed on iron and iron-containing materials by low-temperature oxidation in the presence of water.
b. Any of various metallic coatings, especially oxides, formed by corrosion.
c. A stain or coating resembling iron rust.
2. Deterioration, as of ability, resulting from inactivity or neglect.
3. Botany
a. Rust fungus.
b. A plant disease caused by a rust fungus, characterized by reddish or brownish spots on leaves, stems, and other parts.
4. A strong brown.
v. rust·ed, rust·ing, rusts
v.intr.
1. To become corroded.
2. To deteriorate or degenerate through inactivity or neglect: My golf game has rusted from all those years of not playing.
3. To become the color of rust.
4. Botany To develop a disease caused by a rust fungus.
v.tr.
1. To corrode or subject (a metal) to rust formation.
2. To impair or spoil, as by misuse or inactivity.
3. To color (something) a strong brown.
[Middle English, from Old English rūst; see reudh- in the Appendix of Indo-European roots.]
rust adj.
rusta·ble adj.