The Collaborative International Dictionary of English v.0.48:

Penology \Pe*nol"o*gy\, n. [Gr. poinh`, or L. poena, punishment
   + -logy.]
   The science or art of punishment. [Written also
   p[oe]nology.]
   [1913 Webster]

WordNet (r) 3.0 (2006):

penology
    n 1: the branch of criminology concerned with prison management
         and prisoner rehabilitation [syn: penology, poenology]

Moby Thesaurus II by Grady Ward, 1.0:

26 Moby Thesaurus words for "penology":
   castigation, chastening, chastisement, condign punishment,
   correction, deserts, disciplinary measures, discipline, ferule,
   infliction, judgment, judicial punishment, nemesis, pains,
   pains and punishments, pay, payment, penal retribution, penalty,
   punishment, punition, retribution, retributive justice, scourge,
   well-deserved punishment, what-for