firm vs tough

firm

adj
  • Steadfast, secure, solid (in position) 

  • Durable, rigid (material state) 

  • Fixed (in opinion). 

  • Insistent upon something, not accepting dissent. 

noun
  • A criminal gang, especially based around football hooliganism. 

  • A business partnership; the name under which it trades. 

  • A business enterprise, however organized. 

verb
  • To become firm; stabilise. 

  • To make firm or strong; fix securely. 

  • To improve after decline. 

  • To make compact or resistant to pressure; solidify. 

  • To shorten (of betting odds). 

  • To select (a higher education institution) as one's preferred choice, so as to enrol automatically if one's grades match the conditional offer. 

tough

adj
  • Strong and resilient; sturdy. 

  • Harsh or severe. 

  • Difficult or demanding. 

  • Stubborn or persistent; capable of stubbornness or persistence. 

  • Undergoing plastic deformation before breaking. 

  • Difficult to cut or chew. 

  • Rugged or physically hardy. 

  • Rowdy or rough. 

verb
  • To endure. 

  • To toughen. 

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

intj
  • Used to indicate lack of sympathy 

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