Source : Webster's Revised Unabridged Dictionary (1913)

Simpleness \Sim"ple*ness\, n.
   The quality or state of being simple; simplicity. --Shak.

Source : WordNet®

simpleness
     n : the quality of being simple or uncompounded; "the simplicity
         of a crystal" [syn: {simplicity}] [ant: {complexity}]