The Collaborative International Dictionary of English v.0.48:

Thanatology \Than`a*tol"o*gy\ (th[a^]n`[.a]*t[o^]l"[-o]*j[y^]),
   n. [Gr. qa`natos + -logy.]
   A description, or the doctrine, of death. --Dunglison.
   [1913 Webster]

WordNet (r) 3.0 (2006):

thanatology
    n 1: the branch of science that studies death (especially its
         social and psychological aspects)