backset vs stumbling block

backset

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

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

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

stumbling block

noun
  • A hindrance, obstacle or impediment; an opportunity for error. 

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