emir vs ruler

emir

noun
  • A prince, commander or other leader or ruler in an Islamic nation. 

  • A descendant of the prophet Muhammad. 

ruler

noun
  • A person who rules or governs; someone or something that exercises dominion or controlling power over others. 

  • A (usually rigid), flat, rectangular measuring or drawing device with graduations in units of measurement; a straightedge with markings. 

verb
  • To beat with a ruler (as a traditional school punishment). 

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