earlier vs prior

earlier

adv
  • previously; before now; sooner 

adj
  • occurring previously 

prior

adv
  • Previously. 

adj
  • Former, previous. 

  • Advance; previous; coming before. 

noun
  • A high-ranking member of a monastery, usually lower in rank than an abbot. 

  • A prior probability distribution, one based on information or belief before additional data is collected. 

  • A belief supported by previous evidence or experience that one can use to make inferences about the future. 

  • A chief magistrate in Italy. 

  • A previous arrest or criminal conviction on someone's record. 

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