about-turn vs backtracking

about-turn

noun
  • Total reversal of opinion or attitude. 

  • A turn of 180 degrees, typically in a military formation. 

verb
  • To turn 180 degrees, typically in a military formation. 

backtracking

noun
  • The act of one who, or that which, backtracks; a retracing of one's steps. 

  • The usage of a runway as a taxiway, especially at private strips and smaller airports. 

  • The act of building all possible solutions to a problem incrementally, abandoning any candidate solution if it cannot lead to a valid solution. 

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