Source : Webster's Revised Unabridged Dictionary (1913)

Impracticableness \Im*prac"ti*ca*ble*ness\, n.
   The state or quality of being impracticable;
   impracticability.

Source : WordNet®

impracticableness
     n : the quality of not being usable [syn: {impracticability}]
         [ant: {practicability}, {practicability}]