Source : Webster's Revised Unabridged Dictionary (1913)

Usefulness \Use"ful*ness\, n.
   The quality or state of being useful; utility;
   serviceableness; advantage. --Addison.

   Syn: Utility; value; profit. See {Utility}.

Source : WordNet®

usefulness
     n : the quality of being of practical use [syn: {utility}] [ant:
          {inutility}, {inutility}]