The Collaborative International Dictionary of English v.0.48:

Nosology \No*sol"o*gy\, n. [Gr. no`sos disease + -logy: cf. F.
   nosologie.]
   1. A systematic arrangement, or classification, of diseases.
      [1913 Webster]

   2. That branch of medical science which treats of diseases,
      or of the classification of diseases.
      [1913 Webster]

The Collaborative International Dictionary of English v.0.48:

pathology \pa*thol"o*gy\ (-j[y^]), n.; pl. pathologies
   (-j[i^]z). [Gr. pa`qos a suffering, disease + -logy: cf. F.
   pathologie.]
   1. (Med.) The science which treats of diseases, their nature,
      causes, progress, symptoms, etc.
      [1913 Webster]

   Note: Pathology is general or special, according as it treats
         of disease or morbid processes in general, or of
         particular diseases; it is also subdivided into
         internal and external, or medical and surgical
         pathology. Its departments are nosology,
         [ae]tiology, morbid anatomy, symptomatology, and
         therapeutics, which treat respectively of the
         classification, causation, organic changes, symptoms,
         and cure of diseases.
         [1913 Webster]

   2. (Med.) The condition of an organ, tissue, or fluid
      produced by disease.
      [Webster 1913 Suppl.]

   Celluar pathology, a theory that gives prominence to the
      vital action of cells in the healthy and diseased
      functions of the body. --Virchow.
      [1913 Webster]

WordNet (r) 3.0 (2006):

nosology
    n 1: the branch of medical science dealing with the
         classification of disease [syn: nosology, diagnostics]