The Collaborative International Dictionary of English v.0.48:

Criminology \Crim`i*nol"o*gy\ (-n?l"?-j?), n. [L. crimen,
   crimenis, crime + -logy.]
   1. A treatise on crime or the criminal population.
      [1913 Webster]

   2. The branch of sociology which studies crime and criminals.
      [PJC] -- Crim`i*nol"o*gist (-j?st), n.
      [1913 Webster]

WordNet (r) 3.0 (2006):

criminology
    n 1: the scientific study of crime and criminal behavior and law
         enforcement