The Collaborative International Dictionary of English v.0.48:

pathologist \pa*thol"o*gist\, n. [Cf. F. pathologiste.]
   One skilled in pathology; an investigator in pathology; as,
   the pathologist of a hospital, whose duty it is to determine
   the causes of the diseases.
   [1913 Webster]

WordNet (r) 3.0 (2006):

pathologist
    n 1: a doctor who specializes in medical diagnosis [syn:
         diagnostician, pathologist]