let go vs unloose

let go

verb
  • To release from one's grasp; to go from a state of holding on to a state of no longer holding on. 

  • To dismiss from employment. 

  • To ignore (a comment, etc.). 

  • To emotionally disengage or to distract oneself from a situation. 

  • To fail to maintain a standard of appearance, behavior, or performance. 

  • Used other than figuratively or idiomatically: see let, go. 

  • To gain weight 

unloose

verb
  • To free (someone or something) from a constraint; (figuratively) to release (something which has been suppressed, such as emotions or objectionable things). 

  • To loosen or undo (something that entangles, fastens, holds, or interlocks). 

  • To relax or slacken (something that clasps or grips, such as the arms or hands). 

  • To become loose or come off. 

  • To free from a constraint. 

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