Source : Webster's Revised Unabridged Dictionary (1913)

Psychology \Psy*chol"o*gy\, n. pl. {Psychologies}. [Psycho- +
   -logy: cf. F. psychologie. See {Psychical}.]
   The science of the human soul; specifically, the systematic
   or scientific knowledge of the powers and functions of the
   human soul, so far as they are known by consciousness; a
   treatise on the human soul.

         Psychology, the science conversant about the phenomena
         of the mind, or conscious subject, or self. --Sir W.
                                                  Hamilton.

Source : WordNet®

psychology
     n : the science of mental life [syn: {psychological science}]