rogation vs supplication

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. 

supplication

noun
  • A prayer or entreaty to a god. 

  • The process by which a doctorate at Oxford university is officially requested after a thesis has been approved. 

  • In Ancient Rome, a solemn service or day decreed for giving formal thanks to the gods for victory, etc. 

  • An act of supplicating; a humble request. 

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