mettle vs weakness

mettle

adj
  • Spirited, vigorous, stout-hearted. 

noun
  • Good temperament and character. 

  • A quality of endurance and courage. 

weakness

noun
  • An inadequate quality; fault 

  • The condition of being weak. 

  • A special fondness or desire. 

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