Source : Webster's Revised Unabridged Dictionary (1913)

Variableness \Va"ri*a*ble*ness\, n.
   The quality or state of being variable; variability. --James
   i. 17.

Source : WordNet®

variableness
     n : the quality of being subject to variation [syn: {variability},
          {variance}] [ant: {invariability}, {invariability}]