The Collaborative International Dictionary of English v.0.48:

Morbidity \Mor*bid"i*ty\, n.
   1. The quality or state of being morbid.
      [1913 Webster]

   2. Morbid quality; disease; sickness. --C. Kingsley.
      [1913 Webster]

   3. Amount of disease; rate of sickness.
      [1913 Webster]

WordNet (r) 3.0 (2006):

morbidity
    n 1: the relative incidence of a particular disease
    2: an abnormally gloomy or unhealthy state of mind; "his fear of
       being alone verges on morbidity" [syn: morbidity,
       morbidness]
    3: the quality of being unhealthful and generally bad for you
       [syn: unwholesomeness, morbidness, morbidity] [ant:
       wholesomeness]

Moby Thesaurus II by Grady Ward, 1.0:

102 Moby Thesaurus words for "morbidity":
   abnormality, acute disease, affection, affliction, ailment,
   allergic disease, allergy, atrophy, bacterial disease,
   birth defect, blight, cachexia, cachexy, cardiovascular disease,
   chronic disease, chronic ill health, circulatory disease,
   complaint, complication, condition, congenital defect,
   debilitation, debility, decrepitude, defect, deficiency disease,
   deformity, degenerative disease, delicacy, delicate health,
   disability, disease, disorder, distemper, endemic, endemic disease,
   endocrine disease, enervation, epidemic disease, exhaustion,
   feebleness, fragility, frailty, functional disease, fungus disease,
   gastrointestinal disease, genetic disease, handicap,
   healthlessness, hereditary disease, hypochondria, hypochondriasis,
   iatrogenic disease, ill health, illness, indisposition,
   infectious disease, infirmity, invalidism, invalidity, languishing,
   languishment, malady, malaise, morbidness, morbus,
   muscular disease, neurological disease, nutritional disease,
   occupational disease, organic disease, pandemic disease,
   pathological condition, pathology, peakedness, plant disease,
   poor health, protozoan disease, psychosomatic disease,
   respiratory disease, rockiness, secondary disease, seediness,
   sickishness, sickliness, sickness, signs, symptomatology,
   symptomology, symptoms, syndrome, the pip, unhealthiness,
   unsoundness, unwholesomeness, urogenital disease,
   valetudinarianism, virus disease, wasting, wasting disease,
   weakliness, worm disease