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]

Moby Thesaurus II by Grady Ward, 1.0:

134 Moby Thesaurus words for "ameliorate":
   accommodate, acculturate, adapt, adjust, advance, alleviate, alter,
   amend, be changed, be converted into, be renewed, better, boost,
   bottom out, break, break up, bring forward, change, checker, chop,
   chop and change, civilize, come about, come along, come around,
   come on, come round, convalesce, convert, deform, degenerate,
   denature, deteriorate, develop, deviate, diverge, diversify, edify,
   educate, elevate, emend, enhance, enlighten, enrich, fatten, favor,
   fit, flop, forward, foster, gain, gain ground, get ahead,
   get along, go ahead, go forward, go straight, graduate,
   grow better, haul around, help, improve, improve upon, jibe, lard,
   lift, lighten, look up, make an improvement, make headway,
   make progress, make strides, meliorate, mend, mitigate, modify,
   modulate, mutate, nurture, overthrow, perk up, pick up, progress,
   promote, qualify, raise, re-create, realign, rebuild, reconstruct,
   recuperate, redesign, refine upon, refit, reform, relieve, remake,
   renew, reshape, restructure, revamp, revive, ring the changes,
   shape up, shift, shift the scene, show improvement,
   shuffle the cards, skyrocket, socialize, straighten out, subvert,
   swerve, tack, take a turn, take off, transfigure, transform, turn,
   turn aside, turn into, turn the corner, turn the scale,
   turn the tables, turn the tide, turn upside down, undergo a change,
   upgrade, uplift, vary, veer, warp, work a change, worsen