retard vs set back

retard

verb
  • To keep delaying; to continue to hinder; to prevent from progressing. 

  • To put off; to postpone. 

  • To decelerate; to slow down. 

noun
  • Retardation; delay. 

  • A slowing down of the tempo; a ritardando. 

  • A person or being who is extremely stupid or slow to learn. 

set back

verb
  • To delay or obstruct. 

  • To remove from or allow distance. 

  • To install or position behind a boundary or surface, or in a recess. 

  • To cost money. 

  • To reverse, go backwards. 

How often have the words retard and set back occurred in a corpus of books? (source: Google Ngram Viewer )