opus vs speller

opus

noun
  • A work, especially of art. 

  • A work of music or set of works with a specified rank in an ordering of a composer's complete published works. 

speller

noun
  • A person who spells. 

  • A spell checker. 

  • A participant in a spelling bee. 

  • A book used to learn how to spell properly. 

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