The Collaborative International Dictionary of English v.0.48:

malady \mal"a*dy\ (m[a^]l"[.a]*d[y^]), n.; pl. Maladies
   (m[a^]l"[.a]*d[i^]z). [F. maladie, fr. malade ill, sick, OF.
   also, malabde, fr. L. male habitus, i. e., ill-kept, not in
   good condition. See Malice, and Habit.]
   1. Any disease of the human body; a distemper, disorder, or
      indisposition, proceeding from impaired, defective, or
      morbid organic functions; especially, a lingering or
      deep-seated disorder.
      [1913 Webster]

            The maladies of the body may prove medicines to the
            mind.                                 --Buckminster.
      [1913 Webster]

   2. A moral or mental defect or disorder.
      [1913 Webster]

            Love's a malady without a cure.       --Dryden.
      [1913 Webster]

   Syn: Disorder; distemper; sickness; ailment; disease;
        illness. See Disease.
        [1913 Webster]

WordNet (r) 3.0 (2006):

malady
    n 1: any unwholesome or desperate condition; "what maladies
         afflict our nation?"
    2: impairment of normal physiological function affecting part or
       all of an organism [syn: illness, unwellness, malady,
       sickness] [ant: health, wellness]

Moby Thesaurus II by Grady Ward, 1.0:

72 Moby Thesaurus words for "malady":
   abnormality, acute disease, affection, affliction, ailment,
   allergic disease, allergy, atrophy, bacterial disease,
   birth defect, blight, cardiovascular disease, chronic disease,
   circulatory disease, complaint, complication, condition,
   congenital defect, defect, deficiency disease, deformity,
   degenerative disease, disability, disease, disorder, distemper,
   endemic, endemic disease, endocrine disease, epidemic disease,
   functional disease, fungus disease, gastrointestinal disease,
   genetic disease, handicap, hereditary disease, iatrogenic disease,
   ill, illness, indisposition, infectious disease, infirmity,
   malaise, morbidity, morbus, muscular disease, neurological disease,
   nutritional disease, occupational disease, organic disease,
   pandemic disease, pathological condition, pathology, plant disease,
   protozoan disease, psychosomatic disease, respiratory disease,
   rockiness, secondary disease, seediness, sickishness, sickness,
   signs, symptomatology, symptomology, symptoms, syndrome, the pip,
   urogenital disease, virus disease, wasting disease, worm disease