opus vs pamphlet

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. 

pamphlet

noun
  • Such a work containing political material or discussing matters of controversy. 

  • A small, brief printed work, consisting either of a folded sheet of paper, or several sheets bound together into a booklet with only a paper cover, formerly containing literary compositions, newsletters, and newspapers, but now chiefly informational matter. 

verb
  • To distribute pamphlets (to someone or some place). 

  • To distribute pamphlets. 

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