imperatorial vs mandatory

imperatorial

adj
  • Commanding; authoritative. 

  • Relating to the title or office of imperator. 

mandatory

adj
  • Obligatory; required or commanded by authority. 

  • Of, being or relating to a mandate. 

noun
  • A sign or line that require the path of the disc to be above, below or to one side of it. 

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