duffer vs past master

duffer

noun
  • An incompetent, indolent, or clumsy person. 

  • Any of various nymphalid butterflies of the genus Discophora. 

  • A player having little skill, especially a golfer who duffs. 

  • A racing pigeon that does not perform well. 

  • A cow that does not produce milk. 

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 duffer and past master occurred in a corpus of books? (source: Google Ngram Viewer )