cool down vs restrict

cool down

verb
  • To decrease in degree or intensity. 

  • To become cooler; to be reduced in temperature. 

  • To become less agitated or excited. 

  • To cause (something) to become cooler; to reduce the temperature of. 

  • To cause (someone) to become less agitated or excited. 

restrict

verb
  • To restrain within boundaries; to limit; to confine 

  • To consider (a function) as defined on a subset of its original domain. 

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