specter vs steelhead

specter

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

  • A ghostly apparition, a phantom. 

  • A threatening mental image. 

steelhead

noun
  • The anadromous form of the rainbow trout, Oncorhynchus mykiss. 

  • The ruddy duck. 

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