eidolon vs undead

eidolon

noun
  • A phantom, a ghost or elusive entity. 

  • An image or representation of an idea; a representation of an ideal form; an apparition of some actual or imaginary entity, or of some aspect of reality. 

  • An unsubstantial image, spectre, phantom. 

undead

noun
  • A creature that is undead; that is, dead but still animate. 

  • Those creatures which are undead; that is, dead yet still animate. 

adj
  • Being animate, though non-living. 

  • Pertaining to a corpse, though having qualities of life. 

How often have the words eidolon and undead occurred in a corpus of books? (source: Google Ngram Viewer )