imperatorial vs regnant

imperatorial

adj
  • Commanding; authoritative. 

  • Relating to the title or office of imperator. 

regnant

adj
  • Reigning, ruling; currently holding power. 

  • Dominant; holding sway; having particular power or influence. 

  • of a monarch, ruling in one's one right; often contrasted with consort and dowager 

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