The Collaborative International Dictionary of English v.0.48:

Qualm \Qualm\, n. [AS. cwealm death, slaughter, pestilence, akin
   to OS. & OHG. qualm. See Quail to cower.]
   1. Sickness; disease; pestilence; death. [Obs.]
      [1913 Webster]

            thousand slain and not of qualm ystorve [dead].
                                                  --Chaucer.
      [1913 Webster]

   2. A sudden attack of illness, faintness, or pain; an agony.
      " Qualms of heartsick agony." --Milton.
      [1913 Webster]

   3. Especially, a sudden sensation of nausea.
      [1913 Webster]

            For who, without a qualm, hath ever looked
            On holy garbage, though by Homer cooked?
                                                  --Roscommon.
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   4. A prick or scruple of conscience; uneasiness of
      conscience; compunction. --Dryden.
      [1913 Webster]

WordNet (r) 3.0 (2006):

qualm
    n 1: uneasiness about the fitness of an action [syn: scruple,
         qualm, misgiving]
    2: a mild state of nausea [syn: queasiness, squeamishness,
       qualm]

Moby Thesaurus II by Grady Ward, 1.0:

107 Moby Thesaurus words for "qualm":
   agitation, airsickness, all-overs, anxiety, apprehension,
   apprehensiveness, bashfulness, beef, better self, bitch, boggle,
   boggling, boycott, car sickness, challenge, complaint, compunction,
   concern, conscience, conscientiousness, conviction, demonstration,
   demur, demurral, demurrer, diffidence, disinclination, doubt,
   exception, expostulation, falter, faltering, fastidiousness,
   foreboding, funny feeling, grievance, grievance committee,
   hesitance, hesitancy, hesitation, howl, impatience,
   indignation meeting, insecurity, kick, mal de mer, march,
   meticulousness, misgiving, mistrust, modesty, motion sickness,
   nausea, nervousness, nonviolent protest, objection,
   overconscientiousness, overscrupulousness, pang, pangs,
   pangs of conscience, pause, perturbation, picketing,
   point of honor, presentiment, pricking of heart, protest,
   protest demonstration, protestation, punctilio, punctiliousness,
   qualm of conscience, qualmishness, qualms, queasiness, rally,
   recoil, reluctance, remonstrance, remonstration, scruple, scruples,
   scrupulosity, scrupulousness, seasickness, second thought,
   shrinking, shyness, sit-in, squawk, squeamishness, stickling,
   strike, suspicion, teach-in, throes, touch of conscience, twinge,
   twinge of conscience, uncertainty, unease, uneasiness,
   unwillingness, voice of conscience, vomiting, worry