The Collaborative International Dictionary of English v.0.48:

Considerably \Con*sid"er*a*bly\, adv.
   In a manner or to a degree not trifling or unimportant;
   greatly; much.
   [1913 Webster]

         The breeds . . . differ considerably from each other.
                                                  --Darwin.
   [1913 Webster]

WordNet (r) 3.0 (2006):

considerably
    adv 1: to a great extent or degree; "I'm afraid the film was
           well over budget"; "painting the room white made it seem
           considerably (or substantially) larger"; "the house has
           fallen considerably in value"; "the price went up
           substantially" [syn: well, considerably,
           substantially]

Moby Thesaurus II by Grady Ward, 1.0:

32 Moby Thesaurus words for "considerably":
   a deal, a great deal, a lot, abundantly, as all creation,
   as all get-out, beaucoup, considerable, ever so, ever so much, far,
   galore, greatly, highly, in great measure, largely, much, muchly,
   never so, no end, no end of, not a little, plenty, pretty much,
   quite, rather, significantly, so, so very much, somewhat,
   to the skies, very much