The Collaborative International Dictionary of English v.0.48:

Amelioration \A*mel`io*ra"tion\, n. [Cf. F. am['e]lioration.]
   The act of ameliorating, or the state of being ameliorated;
   making or becoming better; improvement; melioration.
   "Amelioration of human affairs." --J. S. Mill.
   [1913 Webster]

WordNet (r) 3.0 (2006):

amelioration
    n 1: the act of relieving ills and changing for the better [syn:
         amelioration, melioration, betterment]