atabeg vs proconsul

atabeg

noun
  • A high medieval Turkish feudal title, originally charged with the caretaking and mentoring of the realm's crown prince. 

proconsul

noun
  • A magistrate who served as a consul and then as the governor of a province. 

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