former vs prior

former

adj
  • Previous. 

  • First of aforementioned two items. Used with the, often without a noun. 

noun
  • An object used to form something, such as a template, gauge, or cutting die. 

  • Someone who forms something; a maker; a creator or founder. 

  • Someone in, or of, a certain form (class). 

prior

adj
  • Former, previous. 

  • Advance; previous; coming before. 

adv
  • Previously. 

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 former and prior occurred in a corpus of books? (source: Google Ngram Viewer )