The Collaborative International Dictionary of English v.0.48:

Painful \Pain"ful\, a.
   1. Full of pain; causing uneasiness or distress, either
      physical or mental; afflictive; disquieting; distressing.
      --Addison.
      [1913 Webster]

   2. Requiring labor or toil; difficult; executed with
      laborious effort; as a painful service; a painful march.
      [1913 Webster]

   3. Painstaking; careful; industrious. [Obs.] --Fuller.
      [1913 Webster]

            A very painful person, and a great clerk. --Jer.
                                                  Taylor.
      [1913 Webster]

            Nor must the painful husbandman be tired. --Dryden.
      [1913 Webster]

   Syn: Disquieting; troublesome; afflictive; distressing;
        grievous; laborious; toilsome; difficult; arduous.
        [1913 Webster] -- Pain"ful*ly, adv. --
        Pain"ful*ness, n.
        [1913 Webster]

WordNet (r) 3.0 (2006):

painfully
    adv 1: unpleasantly; "his ignorance was painfully obvious" [syn:
           painfully, distressingly]
    2: in or as if in pain; "she moved painfully forward"; "sorely
       wounded" [syn: painfully, sorely] [ant: painlessly]

Moby Thesaurus II by Grady Ward, 1.0:

76 Moby Thesaurus words for "painfully":
   abominably, agonizingly, arduously, awfully, badly, baldly,
   balefully, bitterly, blatantly, brashly, confoundedly, cruelly,
   damnably, deadly, deathly, deplorably, deucedly, difficultly,
   disagreeably, distressfully, distressingly, dolorously, dreadfully,
   egregiously, excessively, excruciatingly, exorbitantly,
   extravagantly, flagrantly, frightfully, grievously, hardly,
   harrowingly, harshly, heartbreakingly, hellishly, horribly,
   improperly, inexcusably, infernally, inordinately, intolerably,
   laboriously, lamentably, miserably, nakedly, openly, pathetically,
   piteously, pitiably, rigorously, roughly, ruefully, sadly,
   severely, shatteringly, shockingly, something awful,
   something fierce, sorely, staggeringly, strenuously, terribly,
   the hard way, toilsomely, torturously, unashamedly, unbearably,
   unconscionably, unduly, unfortunately, unhappily, unpardonably,
   with difficulty, with much ado, woefully