n. The red or orange-yellow coating which is formed on the surface of iron when exposed to air and moisture; red oxid of iron; in an extended sense, any metallic oxid forming a coat on the metal.n. In metal-working, a composition of iron-filings and sal ammoniac, with sometimes a little sulphur, moistened with water and used for filling fast joints.n. In botany, a fungous growth on plants which resembles rust on metal; plant-disease caused by fungi of the class Uredineæ (which see, for special characterization): same as brand, 6. See Fungi, mildew, Puccinia, and Trichobasis; also black rust and red rust, below.n. Any foul extraneous matter; a corrosive, injurious, or disfiguring accretion.n. Any growth, influence, or habit tending to injure the mental or moral faculties; a habit or tendency which clogs action or usefulness; also, the state of being affected with such a habit.To contract or gather rust; be oxidized.To assume an appearance of rust, or as if coated with rust.To degenerate in idleness; become dull through inaction.To cause to contract rust.To impair by time and inactivity.An obsolete variant of roost.n. Rust formed on iron by exposure to air and water often approaches pretty closely in composition the mineral limonite, a ferric oxyhydroxid (Fe4O3(HO)6). It also frequently contains some ferrous or ferrosoferric oxid and hydroxid, and is more or less perceptibly magnetic.