immortality is the condition of never having died and being unable to die, as an amortal entity was never alive to begin with.[1]
Poltergeists are presumably immortal, as they have been described as "indestructible spirits of chaos," and are known to differ from ghosts in that they were never alive at one time.[2]
As immortality refers to entities that have never been alive from the beginning, it is different from "immortality", which means a living being gaining the impossibility to die.