Source : Webster's Revised Unabridged Dictionary (1913)

Rusty \Rust"y\, a. [AS. rustig.] [Compar. {Rustier}; superl.
   {Rustiest.}]
   1. Covered or affected with rust; as, a rusty knife or sword;
      rusty wheat.

   2. Impaired by inaction, disuse, or neglect.

Source : WordNet®

rusty
     adj 1: covered with or consisting of rust; "a rusty machine";
            "rusty deposits"
     2: of the color of rust [syn: {rust}]
     3: impaired in skill by neglect [syn: {out of practice(p)}]
     4: ancient; "hoary jokes" [syn: {hoary}]
     [also: {rustiest}, {rustier}]

rustier
     See {rusty}