impel vs unhorse

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. 

unhorse

verb
  • To disrupt or unseat; to remove from a position. 

  • To forcibly remove from a horse. 

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