elector vs head of state

elector

noun
  • A person eligible to vote in an election; a member of an electorate, a voter. 

  • A member of an electoral college; specifically (US) an official selected by a state as a member of the Electoral College to elect the president and vice president of the United States. 

  • A person eligible to vote to elect a Member of Parliament. 

head of state

noun
  • The chief public representative of a nation having duties, privileges and responsibilities varying greatly depending on the constitutional rules; a monarch in a monarchy, and often styled president in a republic, but variations such as collegiality exist. 

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