The Collaborative International Dictionary of English v.0.48:

Better \Bet"ter\, v. t. [imp. & p. p. Bettered; p. pr. & vb.
   n. Bettering.] [AS. beterian, betrian, fr. betera better.
   See Better, a.]
   1. To improve or ameliorate; to increase the good qualities
      of.
      [1913 Webster]

            Love betters what is best.            --Wordsworth.
      [1913 Webster]

            He thought to better his circumstances. --Thackeray.
      [1913 Webster]

   2. To improve the condition of, morally, physically,
      financially, socially, or otherwise.
      [1913 Webster]

            The constant effort of every man to better himself.
                                                  --Macaulay.
      [1913 Webster]

   3. To surpass in excellence; to exceed; to excel.
      [1913 Webster]

            The works of nature do always aim at that which can
            not be bettered.                      --Hooker.
      [1913 Webster]

   4. To give advantage to; to support; to advance the interest
      of. [Obs.]
      [1913 Webster]

            Weapons more violent, when next we meet,
            May serve to better us and worse our foes. --Milton.
      [1913 Webster]

   Syn: To improve; meliorate; ameliorate; mend; amend; correct;
        emend; reform; advance; promote.
        [1913 Webster]

Moby Thesaurus II by Grady Ward, 1.0:

19 Moby Thesaurus words for "bettered":
   advanced, ameliorated, beautified, civilized, converted,
   cultivated, cultured, developed, educated, embellished, enhanced,
   enriched, improved, perfected, polished, refined, reformed,
   transfigured, transformed