Source : Webster's Revised Unabridged Dictionary (1913)

Rust \Rust\, v. i. [imp. & p. p. {Rusted}; p. pr. & vb. n.
   {Rusting}.] [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. Fig.: 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.

Source : WordNet®

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