Rust

1. Any of various powdery or scaly reddish-brown or reddish-yellow hydrated ferric oxides formed on iron and iron-containing materials by low-temperature oxidation in the presence of water. Iron will rust if left out in the rain.
2. Deterioration, as of ability, resulting from inactivity or neglect. He, after a long while, became quite rusty in doing auto repairs.
3. Color. A strong brown. She ordered the stove in a rust finish.