1. The condition of being coated or clogged with rust
   "The rustiness of the old tools made them difficult to use"
    
2. Ineptitude or awkwardness as a consequence of age or lack of practice
   "his rustiness showed when he was asked to speed up"

Type of: awkwardness, cack-handedness [Brit, informal], clumsiness, condition, ineptitude, ineptness, maladroitness, slowness, status