death instinct
in psychoanalytic theory, a drive whose aim is the reduction of psychical tension to the lowest possible point, that is, death. It is first directed inward as a self-destructive tendency and is later turned outward in the form of the aggressive instinct. In the dual instinct theory of Sigmund Freud, the death instinct, or Thanatos, stands opposed to the life instinct, or Eros, and is believed to be the drive underlying such behaviors as aggressiveness, sadism, and masochism. See also nirvana principle.