exoneration vs let-off

exoneration

noun
  • The state of being disburdened or freed from a charge. 

  • An act of disburdening, discharging, or freeing morally from a charge or imputation. 

let-off

noun
  • An escape from punishment. 

  • A device for letting off, releasing, or giving forth, as the warp from the cylinder of a loom. 

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