The Collaborative International Dictionary of English v.0.48:

Considerable \Con*sid"er*a*ble\ (k[o^]n*s[i^]d"[~e]r*[.a]*b'l),
   a. [Cf. F. consid['e]rable.]
   1. Worthy of consideration; requiring to be observed, borne
      in mind, or attended to.
      [1913 Webster]

            It is considerable, that some urns have had
            inscriptions on them expressing that the lamps were
            burning.                              --Bp. Wilkins.
      [1913 Webster]

            Eternity is infinitely the most considerable
            duration.                             --Tillotson.
      [1913 Webster]

   2. Of some distinction; noteworthy; influential; respectable;
      -- said of persons.
      [1913 Webster]

            You are, indeed, a very considerable man. --Junius.
      [1913 Webster]

   3. Of importance or value.
      [1913 Webster]

            In painting, not every action, nor every person, is
            considerable enough to enter into the cloth.
                                                  --Dryden.
      [1913 Webster]

            A considerable sum of money.          --Prescott.
      [1913 Webster]

WordNet (r) 3.0 (2006):

considerable
    adj 1: large or relatively large in number or amount or extent
           or degree; "a considerable quantity"; "the economy was a
           considerable issue in the campaign"; "went to
           considerable trouble for us"; "spent a considerable
           amount of time on the problem" [ant: inconsiderable]