The Collaborative International Dictionary of English v.0.48:

Post-mortem \Post-mor"tem\, a. [L., after death.]
   After death; as, post-mortem rigidity.
   [1913 Webster]

   Post-mortem examination (Med.), an examination of the body
      made after the death of the patient; an autopsy.
      [1913 Webster]

WordNet (r) 3.0 (2006):

postmortem
    adj 1: occurring or done after death; "postmortem changes"; "a
           postmortem examination to determine cause of death";
           "postmortal wounds" [syn: postmortem, postmortal]
           [ant: antemortem]
    2: after death or after an event; "a postmortem examination to
       determine the cause of death"; "the postmortem discussion of
       the President's TV address"
    n 1: discussion of an event after it has occurred [syn:
         postmortem, post-mortem]
    2: an examination and dissection of a dead body to determine
       cause of death or the changes produced by disease [syn:
       autopsy, necropsy, postmortem, post-mortem, PM,
       postmortem examination, post-mortem examination]