regrade vs turn tail

regrade

verb
  • To regroup or reassign. 

  • To change the classification of (potentially secret documentation). 

  • To grade again, give a new grade or grading to. 

noun
  • The act or process of grading again. 

turn tail

verb
  • To turn away from someone or something, in preparation for running away; to reverse direction; to leave or flee. 

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