disengage vs untighten

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 

untighten

verb
  • To loosen; to make something less tight. 

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