Rust (?), n. [AS. rust; akin to D. roest, G. & Sw. rost, Icel. ryð; -- named from its color, and akin to E. red. √113. See Red.] 1. (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.
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2. (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.
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&hand_; Rust is also applied to many other minute fungi which infest vegetation, such as the species of Ustilago, Uredo, and Lecythea.
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3. That which resembles rust in appearance or effects. Specifically: (a) A composition used in making a rust joint. See Rust joint, below. (b) Foul matter arising from degeneration; as, rust on salted meat. (c) Corrosive or injurious accretion or influence.
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Sacred truths cleared from all rust and dross of human mixtures. Eikon Basilike.
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&hand_; Rust is used in the formation of compounds of obvious meaning; as, rust-colored, rust-consumed, rust-eaten, and the like.
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Rust joint, 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. -- Rust mite (Zoöl.), a minute mite (Phytopius oleivorus) which, by puncturing the rind, causes the rust-colored patches on oranges.
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Rust, v. t. 1. To cause to contract rust; to corrode with rust; to affect with rust of any kind.
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Keep up your bright swords, for the dew will rust them. Shak.
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2. Fig.: To impair by time and inactivity. Johnson.
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