1. (n.) The reddish yellow coating formed on iron when exposed to moist air, consisting of ferric oxide or hydroxide; hence, by extension, any metallic film of corrosion.

2. (n.) A minute mold or fungus forming reddish or rusty spots on the leaves and stems of cereal and other grasses (Trichobasis Rubigo-vera), now usually believed to be a form or condition of the corn mildew (Puccinia graminis). As rust, it has solitary reddish spores; as corn mildew, the spores are double and blackish.

3. (n.) That which resembles rust in appearance or effects.

4. (n.) A composition used in making a rust joint. See Rust joint, below.

5. (n.) Foul matter arising from degeneration; as, rust on salted meat.

6. (n.) Corrosive or injurious accretion or influence.

7. (v. i.) To contract rust; to be or become oxidized.

8. (v. i.) To be affected with the parasitic fungus called rust; also, to acquire a rusty appearance, as plants.

9. (v. i.) To degenerate in idleness; to become dull or impaired by inaction.

10. (v. t.) To cause to contract rust; to corrode with rust; to affect with rust of any kind.

11. (v. t.) To impair by time and inactivity.