rustn.[AS. rust; akin to D. roest, G. & Sw. rost, Icel. ry; -- 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.()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.()()3. That which resembles rust in appearance or effects.()Sacred truths cleared from all rust and dross of human mixtures. (Eikon Basilike.)()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 (Zol.), a minute mite (Phytopius oleivorus) which, by puncturing the rind, causes the rust-colored patches on oranges.()v. i.[AS. rustian.]1. To contract rust; to be or become oxidized.()If gold ruste, what shall iron do? (Chaucer.)Our armors now may rust. (Dryden.)2. To be affected with the parasitic fungus called rust; also, to acquire a rusty appearance, as plants.()3. To degenerate in idleness; to become dull or impaired by inaction.()Must I rust in Egypt? never more
Appear in arms, and be the chief of Greece? (Dryden.)v. t.1. To cause to contract rust; to corrode with rust; to affect with rust of any kind.()Keep up your bright swords, for the dew will rust them. (Shak.)2. To impair by time and inactivity.(Johnson.)