opus vs symphony

opus

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

  • A work, especially of art. 

symphony

noun
  • An extended piece of music of sophisticated structure, usually for orchestra. 

  • Harmony in music or colour, or a harmonious combination of elements. 

  • An instrumental introduction or termination to a vocal composition. 

  • A symphony orchestra. 

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