The Collaborative International Dictionary of English v.0.48:

Ameliorate \A*mel"io*rate\, v. t. [imp. & p. p. Ameliorated;
   p. pr. & vb. n. Ameliorating.] [L. ad + meliorare to make
   better: cf. F. am['e]liorer. See Meliorate.]
   To make better; to improve; to meliorate.
   [1913 Webster]

         In every human being there is a wish to ameliorate his
         own condition.                           --Macaulay.
   [1913 Webster]

The Collaborative International Dictionary of English v.0.48:

Ameliorate \A*mel"io*rate\, v. i.
   To grow better; to meliorate; as, wine ameliorates by age.
   [1913 Webster]

WordNet (r) 3.0 (2006):

ameliorate
    v 1: to make better; "The editor improved the manuscript with
         his changes" [syn: better, improve, amend,
         ameliorate, meliorate] [ant: aggravate, exacerbate,
         exasperate, worsen]
    2: get better; "The weather improved toward evening" [syn:
       better, improve, ameliorate, meliorate] [ant:
       decline, worsen]