The Collaborative International Dictionary of English v.0.48:

Psychologist \Psy*chol"o*gist\, n. [Cf. F. psychologiste.]
   One who is versed in, devoted to, psychology.
   [1913 Webster]

WordNet (r) 3.0 (2006):

psychologist
    n 1: a scientist trained in psychology

Moby Thesaurus II by Grady Ward, 1.0:

22 Moby Thesaurus words for "psychologist":
   Adler, Freud, Horney, Pavlov, Reich, Skinner, Watson, alienist,
   clinical psychologist, industrial psychologist, neuropsychiatrist,
   psychiatrist, psychobiologist, psychochemist, psychographer,
   psychologue, psychopathist, psychopathologist, psychophysicist,
   psychophysiologist, psychotechnologist, somatist