1. necropsy-an examination and dissection of a dead body to determine cause of death or the changes produced by disease. autopsy, PM, postmortem examination, post-mortem examination, postmortem, post-mortem.examination, scrutiny-the act of examining something closely (as for mistakes).. necropsy-an examination and dissection of a dead body to determine cause of death or the changes produced by disease. autopsy, PM, postmortem examination, post-mortem examination, postmortem, post-mortem.