opuscule vs speller

opuscule

noun
  • A small or petty work. 

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 opuscule and speller occurred in a corpus of books? (source: Google Ngram Viewer )