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]

The Collaborative International Dictionary of English v.0.48:

aetiology \ae`ti*ol"o*gy\ ([=e]`t[i^]*[o^]l"[-o]*j[y^]), n. [L.
   aetologia, Gr. a'itiologi`a; a'iti`a cause + lo`gos
   description: cf. F. ['e]tiologie.]
   1. The science, doctrine, or demonstration of causes; esp.,
      the investigation of the causes of any disease; the
      science of the origin and development of things; etiology.
      AS
      [1913 Webster]

   2. The assignment of a cause.
      [1913 Webster]

   3. (Med.) The cause or origin of a disease. Now more commonly
      written etiology.
      [PJC + AS]

WordNet (r) 3.0 (2006):

aetiology
    n 1: the cause of a disease [syn: etiology, aetiology]
    2: the philosophical study of causation [syn: etiology,
       aetiology]