Source : Webster's Revised Unabridged Dictionary (1913)

Inflexibleness \In*flex"i*ble*ness\, n.
   The quality or state of being inflexible; inflexibility;
   rigidity; firmness.

Source : WordNet®

inflexibleness
     n : a lack of physical flexibility [syn: {inflexibility}] [ant:
         {flexibility}]