The Collaborative International Dictionary of English v.0.48:

Rust \Rust\, v. i. [imp. & p. p. Rusted; p. pr. & vb. n.
   Rusting.] [AS. rustian.]
   1. To contract rust; to be or become oxidized.
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            If gold ruste, what shall iron do?    --Chaucer.
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            Our armors now may rust.              --Dryden.
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   2. To be affected with the parasitic fungus called rust;
      also, to acquire a rusty appearance, as plants.
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   3. Fig.: To degenerate in idleness; to become dull or
      impaired by inaction.
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            Must I rust in Egypt? never more
            Appear in arms, and be the chief of Greece?
                                                  --Dryden.
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WordNet (r) 3.0 (2006):

rusting
    n 1: the formation of reddish-brown ferric oxides on iron by
         low-temperature oxidation in the presence of water [syn:
         rust, rusting]