quicksilver vs tough

quicksilver

adj
  • Unpredictable, erratic or fickle; mercurial. 

noun
  • The metal mercury. 

  • An amalgam of mercury and tin applied to the backs of mirrors, quicksilvering. 

verb
  • To overlay with quicksilver. 

  • To treat with quicksilver. 

tough

adj
  • Stubborn or persistent; capable of stubbornness or persistence. 

  • Harsh or severe. 

  • Difficult or demanding. 

  • Strong and resilient; sturdy. 

  • Undergoing plastic deformation before breaking. 

  • Difficult to cut or chew. 

  • Rugged or physically hardy. 

  • Rowdy or rough. 

noun
  • A person who obtains things by force; a thug or bully. 

intj
  • Used to indicate lack of sympathy 

verb
  • To endure. 

  • To toughen. 

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