Source : Webster's Revised Unabridged Dictionary (1913)

Amiableness \A`mi*a*ble*ness\, n.
   The quality of being amiable; amiability.

Source : WordNet®

amiableness
     n : a disposition to be friendly and approachable (easy to talk
         to) [syn: {affability}, {affableness}, {amiability}, {bonhomie},
          {geniality}]