chastise vs let off

chastise

verb
  • To punish (someone), especially by corporal punishment. 

  • To castigate; to severely scold or censure (someone). 

  • To lightly criticize or correct (someone). 

let off

verb
  • To forgive and not punish. 

  • To cause to explode or come out; to release. 

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