loosen vs unbolt

loosen

verb
  • To make loose. 

  • To free from restraint; to set at liberty. 

  • To become unfastened or undone. 

  • To relieve (the bowels) from constipation; to promote defecation. 

  • To become loose. 

  • To disengage (a device that restrains). 

unbolt

verb
  • To unlock by undoing the bolts of. 

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