The Collaborative International Dictionary of English v.0.48:

Horribly \Hor"ri*bly\, adv.
   In a manner to excite horror; dreadfully; terribly.
   [1913 Webster]

WordNet (r) 3.0 (2006):

horribly
    adv 1: of a dreadful kind; "there was a dreadfully bloody
           accident on the road this morning" [syn: dreadfully,
           awfully, horribly]

Moby Thesaurus II by Grady Ward, 1.0:

105 Moby Thesaurus words for "horribly":
   abominably, agonizingly, alarmingly, appallingly, astoundingly,
   atrociously, awfully, baldly, balefully, banefully, basely,
   bestially, bitterly, blatantly, brashly, brutally, confoundedly,
   contemptibly, cruelly, damnably, deadly, deathly, despicably,
   detestably, deucedly, direly, disconcertingly, disgustingly,
   dismayingly, distressingly, dolorously, dreadful, dreadfully,
   egregiously, excessively, excruciatingly, exorbitantly,
   extravagantly, fearfully, flagrantly, forbiddingly, foully,
   frightfully, fulsomely, ghastly, grievously, grimly, grossly,
   gruesomely, hellishly, hideously, horrendously, horridly,
   horrifically, horrifyingly, improperly, inexcusably, infamously,
   infernally, inordinately, intolerably, lamentably, loathsomely,
   miserably, nakedly, nastily, nauseatingly, notoriously,
   obnoxiously, odiously, offensively, openly, outrageously,
   painfully, piteously, repugnantly, repulsively, revoltingly, sadly,
   savagely, scandalously, shabbily, shamefully, shatteringly,
   shockingly, something awful, something fierce, sordidly, sorely,
   staggeringly, startlingly, terribly, terrifically, torturously,
   tragically, tremendously, unashamedly, unbearably, unconscionably,
   unduly, unpardonably, viciously, vilely, woefully, wretchedly