The Collaborative International Dictionary of English v.0.48:

physiology \phys`i*ol"o*gy\ (f[i^]z`[i^]*[o^]l"[-o]*j[y^]), n.;
   pl. Physiologies. [L. physiologia, Gr. fysiologi`a; fy`sis
   nature + lo`gos discourse: cf. F. physiologie.]
   1. The science which treats of the phenomena of living
      organisms; the study of the processes incidental to, and
      characteristic of, life.
      [1913 Webster]

   Note: It is divided into animal and vegetable physiology,
         dealing with animal and vegetable life respectively.
         When applied especially to a study of the functions of
         the organs and tissues in man, it is called human
         physiology.
         [1913 Webster]

   2. A treatise on physiology.
      [1913 Webster]

   Mental physiology, the science of the functions and
      phenomena of the mind, as distinguished from a
      philosophical explanation of the same.
      [1913 Webster]

WordNet (r) 3.0 (2006):

physiology
    n 1: the branch of the biological sciences dealing with the
         functioning of organisms
    2: processes and functions of an organism