impel vs retard

impel

verb
  • To drive forward; to propel an object, to provide an impetus for motion or action. 

  • To urge a person; to press on; to incite to action or motion via intrinsic motivation. 

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. 

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