rust

from The American Heritage® Dictionary of the English Language, 5th Edition.

• noun 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.
• noun Any of various metallic coatings, especially oxides, formed by corrosion.
• noun A stain or coating resembling iron rust.
• noun Deterioration, as of ability, resulting from inactivity or neglect.
• noun Rust fungus.
• noun A plant disease caused by a rust fungus, characterized by reddish or brownish spots on leaves, stems, and other parts.
• noun A strong brown.
• intransitive verb To become corroded.
• intransitive verb To deteriorate or degenerate through inactivity or neglect.
• intransitive verb To become the color of rust.
• intransitive verb Botany To develop a disease caused by a rust fungus.
• intransitive verb To corrode or subject (a metal) to rust formation.
• intransitive verb To impair or spoil, as by misuse or inactivity.
• intransitive verb To color (something) a strong brown.

from The Century Dictionary.

• 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.
• noun 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.
• noun 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.
• noun 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.
• noun Any foul extraneous matter; a corrosive, injurious, or disfiguring accretion.
• noun 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.
• noun 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.

from the GNU version of the Collaborative International Dictionary of English.

• noun (Chem.) 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.
• noun (Bot.) 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.
• noun That which resembles rust in appearance or effects.
• noun Foul matter arising from degeneration.
• noun Corrosive or injurious accretion or influence.
• noun a joint made between surfaces of iron by filling the space between them with a wet mixture of cast-iron borings, sal ammoniac, and sulphur, which by oxidation becomes hard, and impervious to steam, water, etc.
• noun (Zoöl.) a minute mite (Phytopius oleivorus) which, by puncturing the rind, causes the rust-colored patches on oranges.
• transitive verb To cause to contract rust; to corrode with rust; to affect with rust of any kind.
• transitive verb To impair by time and inactivity.
• intransitive verb To contract rust; to be or become oxidized.
• intransitive verb To be affected with the parasitic fungus called rust; also, to acquire a rusty appearance, as plants.
• intransitive verb To degenerate in idleness; to become dull or impaired by inaction.

from Wiktionary, Creative Commons Attribution/Share-Alike License.

• noun The deteriorated state of iron or steel as a result of moisture and oxidation.
• noun A reddish-brown color.
• noun A disease of plants caused by a reddish-brown fungus.
• verb intransitive to oxidize, especially of iron or steel.
• verb transitive to cause to oxidize.

from WordNet 3.0 Copyright 2006 by Princeton University. All rights reserved.

• verb become coated with oxide
• verb become destroyed by water, air, or a corrosive such as an acid
• verb cause to deteriorate due to the action of water, air, or an acid
• noun a red or brown oxide coating on iron or steel caused by the action of oxygen and moisture
• noun the formation of reddish-brown ferric oxides on iron by low-temperature oxidation in the presence of water