The Collaborative International Dictionary of English v.0.48:

Unduly \Un*du"ly\, adv.
   In an undue manner.
   [1913 Webster]

WordNet (r) 3.0 (2006):

unduly
    adv 1: to an undue degree; "she was unduly pessimistic about her
           future"

Moby Thesaurus II by Grady Ward, 1.0:

78 Moby Thesaurus words for "unduly":
   abominably, agonizingly, awfully, baldly, balefully, bitterly,
   blatantly, brashly, confoundedly, cruelly, damnably, deadly,
   deathly, deucedly, disproportionately, distressingly, dolorously,
   dreadfully, egregiously, excessively, excruciatingly, exorbitantly,
   extortionately, extravagantly, extremely, flagrantly, frightfully,
   gougingly, grievously, grossly, hellishly, horribly, immensely,
   immoderately, improperly, inappropriately, inexcusably, infernally,
   inordinately, intemperately, intolerably, irrationally, lamentably,
   lavishly, miserably, nakedly, openly, outrageously, over, overfull,
   overly, overmuch, overweeningly, painfully, piteously,
   preposterously, profusely, sadly, shatteringly, shockingly,
   something awful, something fierce, sorely, staggeringly, terribly,
   too, too much, too-too, torturously, unashamedly, unbearably,
   unconscionably, unjustifiably, unnecessarily, unpardonably,
   unreasonably, usuriously, woefully