expert vs past master

expert

noun
  • A person with extensive knowledge or ability in a given subject. 

  • A player ranking just below master. 

adj
  • Extraordinarily capable or knowledgeable. 

  • Characteristic of an expert. 

past master

noun
  • One who has an extremely high level of ability or knowledge within an area of achievement or expertise. 

  • Someone who has previously been a master at a given lodge. 

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