The Collaborative International Dictionary of English v.0.48:

Nephrology \Ne*phrol"o*gy\, n. [Gr. nefro`s a kidney + -logy.]
   A treatise on, or the science which treats of, the kidneys,
   and their structure and functions.
   [1913 Webster]

WordNet (r) 3.0 (2006):

nephrology
    n 1: the branch of medicine concerned with the kidney - its
         development and anatomy and physiology and disorders