cool down vs restrain

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. 

restrain

verb
  • To restrict or limit. 

  • To control or keep in check. 

  • To deprive of liberty. 

  • To strain again. 

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