diffidence vs mettle

diffidence

noun
  • The state of being diffident, timid or shy; reticence or self-effacement. 

mettle

adj
  • Spirited, vigorous, stout-hearted. 

noun
  • Good temperament and character. 

  • A quality of endurance and courage. 

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