specter vs undead

specter

noun
  • A ghostly apparition, a phantom. 

  • Any of certain species of dragonfly of the genus Boyeria, family Aeshnidae. 

  • A threatening mental image. 

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 specter and undead occurred in a corpus of books? (source: Google Ngram Viewer )