mettle vs spinelessness

mettle

noun
  • Good temperament and character. 

  • A quality of endurance and courage. 

adj
  • Spirited, vigorous, stout-hearted. 

spinelessness

noun
  • The state or quality of being spineless (not having a spine (literally or figuratively)); cowardice. 

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