retard vs roll back

retard

verb
  • To put off; to postpone. 

  • To decelerate; to slow down. 

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

noun
  • Retardation; delay. 

  • A slowing down of the tempo; a ritardando. 

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

roll back

verb
  • To postpone. 

  • To return to a prior state. 

  • To reduce thrust without having been commanded to do so. 

  • To retreat. 

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