Source : Webster's Revised Unabridged Dictionary (1913)

Melioration \Mel`io*ra"tion\, n. [L. melioratio.]
   The act or operation of meliorating, or the state of being
   meliorated; improvement. --Bacon.

Source : WordNet®

melioration
     n 1: the act of relieving ills and changing for the better [syn:
          {amelioration}, {betterment}]
     2: a condition superior to an earlier condition; "the new
        school represents a great improvement" [syn: {improvement}]
        [ant: {decline}]
     3: the linguistic process in which over a period of time a word
        grows more positive in connotation or more elevated in
        meaning