The Collaborative International Dictionary of English v.0.48:

Phrenology \Phre*nol"o*gy\, n. [Gr. frh`n, freno`s, the mind +
   -logy: cf. F. phr['e]nologie.]
   1. The science of the special functions of the several parts
      of the brain, or of the supposed connection between the
      various faculties of the mind and particular organs in the
      brain.
      [1913 Webster]

   2. In popular usage, the obsolete physiological hypothesis of
      Gall, that the mental faculties, and traits of character,
      are shown on the surface of the head or skull; craniology.
      it is considered a pseudo-science by all reputable medical
      personnel, but is still believed by some people.

   Syn: craniognomy.
        [1913 Webster + PJC]

   Note: Gall marked out on his model of the head the places of
         twenty-six organs, as round inclosures with vacant
         interspaces. Spurzheim and Combe divided the whole
         scalp into oblong and conterminous patches. --Encyc.
         Brit.
         [1913 Webster]
         [1913 Webster]

WordNet (r) 3.0 (2006):

phrenology
    n 1: a now abandoned study of the shape of skull as indicative
         of the strengths of different faculties

The Devil's Dictionary (1881-1906):

PHRENOLOGY, n.  The science of picking the pocket through the scalp.
It consists in locating and exploiting the organ that one is a dupe
with.