Source : Webster's Revised Unabridged Dictionary (1913)

Betterment \Bet"ter*ment\, n.
   1. A making better; amendment; improvement. --W. Montagu.

   2. (Law) An improvement of an estate which renders it better
      than mere repairing would do; -- generally used in the
      plural. [U. S.] --Bouvier.

Source : WordNet®

betterment
     n 1: a change for the better; progress in development [syn: {improvement},
           {advance}]
     2: an improvement that adds to the value of a property or
        facility
     3: the act of relieving ills and changing for the better [syn:
        {amelioration}, {melioration}]