The Collaborative International Dictionary of English v.0.48:

Terrifically \Ter*rif"ic*al*ly\, adv.
   In a terrific manner.
   [1913 Webster]

WordNet (r) 3.0 (2006):

terrifically
    adv 1: (used as an intensifier) extremely well; "her voice is
           superbly disciplined"; "the colors changed wondrously
           slowly" [syn: wonderfully, wondrous, wondrously,
           superbly, toppingly, marvellously, terrifically,
           marvelously]