backtrack vs turn back

backtrack

verb
  • To retrace one's steps. 

  • To exercise a racehorse around the racetrack in the opposite direction to that in which races are run. 

  • To taxi down an active runway in the opposite direction to that being used for takeoff. 

  • To repeat or review work already done. 

noun
  • the act of backtracking 

turn back

verb
  • To reverse direction and retrace one's steps. 

  • To cause to reverse direction and retrace one's steps. 

  • To return to a previous state of being. 

  • To prevent or refuse to allow passage or progress. 

  • To adjust to a previous setting. 

  • To fold something back; to fold down. 

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