piety vs rogation

piety

noun
  • A devout act or thought. 

  • Reverence and devotion to God. 

  • A belief that is accepted unthinkingly and with undue reverence. 

  • Similar reverence to one's parents and family or to one's country. 

rogation

noun
  • A deeply serious and somber prayer or entreaty. 

  • The demand, by the consuls or tribunes, of a law to be passed by the people; a proposed law or decree. 

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