The Collaborative International Dictionary of English v.0.48:

Improve \Im*prove"\, v. t. [imp. & p. p. Improved; p. pr. &
   vb. n. Improving.] [Pref. in- in + prove, in approve. See
   Approve, Prove.]
   1. To make better; to increase the value or good qualities
      of; to ameliorate by care or cultivation; as, to improve
      land. --Donne.
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            I love not to improve the honor of the living by
            impairing that of the dead.           --Denham.
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   2. To use or employ to good purpose; to make productive; to
      turn to profitable account; to utilize; as, to improve
      one's time; to improve his means. --Shak.
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            We shall especially honor God by improving
            diligently the talents which God hath committed to
            us.                                   --Barrow.
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            A hint that I do not remember to have seen opened
            and improved.                         --Addison.
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            The court seldom fails to improve the opportunity.
                                                  --Blackstone.
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            How doth the little busy bee
            Improve each shining hour.            --I. Watts.
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            Those moments were diligently improved. --Gibbon.
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            True policy, as well as good faith, in my opinion,
            binds us to improve the occasion.     --Washington.
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   3. To advance or increase by use; to augment or add to; --
      said with reference to what is bad. [R.]
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            We all have, I fear, . . . not a little improved the
            wretched inheritance of our ancestors. --Bp.
                                                  Porteus.

   Syn: To better; meliorate; ameliorate; advance; heighten;
        mend; correct; rectify; amend; reform.
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The Collaborative International Dictionary of English v.0.48:

Improve \Im*prove"\, v. t. [Pref. im- not + prove: cf. L.
   improbare, F. improuver.]
   1. To disprove or make void; to refute. [Obs.]
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            Neither can any of them make so strong a reason
            which another can not improve.        --Tyndale.
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   2. To disapprove; to find fault with; to reprove; to censure;
      as, to improve negligence. [Obs.] --Chapman.
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            When he rehearsed his preachings and his doing unto
            the high apostles, they could improve nothing.
                                                  --Tyndale.
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The Collaborative International Dictionary of English v.0.48:

Improve \Im*prove"\, v. i.
   1. To grow better; to advance or make progress in what is
      desirable; to make or show improvement; as, to improve in
      health.
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            We take care to improve in our frugality and
            diligence.                            --Atterbury.
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   2. To advance or progress in bad qualities; to grow worse.
      "Domitian improved in cruelty." --Milner.
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   3. To increase; to be enhanced; to rise in value; as, the
      price of cotton improves.
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   To improve on or To improve upon, to make useful
      additions or amendments to, or changes in; to bring nearer
      to perfection; as, to improve on the mode of tillage.
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WordNet (r) 3.0 (2006):

improve
    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]