The Collaborative International Dictionary of English v.0.48:

Predominantly \Pre*dom"i*nant*ly\, adv.
   In a predominant manner.
   [1913 Webster]

WordNet (r) 3.0 (2006):

predominantly
    adv 1: much greater in number or influence; "the patients are
           predominantly indigenous" [syn: predominantly,
           preponderantly]

Moby Thesaurus II by Grady Ward, 1.0:

49 Moby Thesaurus words for "predominantly":
   a fortiori, above all, all in all, all the more,
   all things considered, altogether, as a rule, as a whole,
   as an approximation, at large, broadly, broadly speaking,
   by and large, chiefly, commonly, dominantly, especially, even,
   ever so, first of all, generally, generally speaking, in chief,
   in general, in the main, indeed, largely, mainly, more than ever,
   mostly, never so, no end, normally, on balance, on the whole,
   ordinarily, overall, particularly, peculiarly, prevailingly,
   primarily, principally, roughly, roughly speaking, routinely,
   speaking generally, still more, usually, yea