fall off vs merge

fall off

verb
  • To diminish in size, value, etc. 

  • To fall into sin; stray. 

  • To change the direction of the sail so as to point in a direction that is more down wind; to bring the bow leeward. 

  • To become detached or to drop from. 

merge

verb
  • To blend gradually into something else. 

  • To combine into a whole. 

noun
  • The joining together of multiple sources. 

How often have the words fall off and merge occurred in a corpus of books? (source: Google Ngram Viewer )