backset vs rear end

backset

noun
  • Whatever is thrown back in its course, such as water. 

  • A check; a relapse; a discouragement; a setback. 

verb
  • To plow again in the fall; said of prairie land broken up in the spring. 

rear end

noun
  • The back or hindmost part of anything, such as a car. 

  • The buttocks. 

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