struggle vs tough

struggle

verb
  • To strive, to labour in difficulty, to fight (for or against), to contend. 

  • To strive, or to make efforts, with a twisting, or with contortions of the body. 

noun
  • A contortion of the body in an attempt to escape or to perform a difficult task. 

  • Strife, contention, great effort. 

tough

verb
  • To toughen. 

  • To endure. 

intj
  • Used to indicate lack of sympathy 

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

adj
  • Harsh or severe. 

  • Difficult or demanding. 

  • Stubborn or persistent; capable of stubbornness or persistence. 

  • Strong and resilient; sturdy. 

  • Undergoing plastic deformation before breaking. 

  • Difficult to cut or chew. 

  • Rugged or physically hardy. 

  • Rowdy or rough. 

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