The Collaborative International Dictionary of English v.0.48:

Substantially \Sub*stan"tial*ly\, adv.
   In a substantial manner; in substance; essentially.
   [1913 Webster]

         In him all his Father shone,
         Substantially expressed.                 --Milton.
   [1913 Webster]

         The laws of this religion would make men, if they would
         truly observe them, substantially religious toward God,
         chastle, and temperate.                  --Tillotson.
   [1913 Webster]

WordNet (r) 3.0 (2006):

substantially
    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]
    2: in a strong substantial way; "the house was substantially
       built"

Moby Thesaurus II by Grady Ward, 1.0:

44 Moby Thesaurus words for "substantially":
   actually, adequately, all in all, almost entirely, amply,
   approximately, at bottom, at heart, at the core, au fond,
   basically, by and large, chiefly, competently, effectually, enough,
   essentially, fundamentally, in essence, in fact, in itself,
   in reality, in substance, in the main, in truth, indeed,
   intrinsically, largely, mainly, materially, minimally, mostly,
   on balance, on the whole, per se, practically, primarily,
   satisfactorily, sincerely, sufficiently, truly, verily, veritably,
   virtually