disengage vs let off

disengage

verb
  • To release or loosen from something that binds, entangles, holds, or interlocks. 

noun
  • A circular movement of the blade that avoids the opponent's parry 

let off

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

  • To forgive and not punish. 

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