bass viol vs contrabass

bass viol

noun
  • A fretted, bowed, stringed musical instrument from the viola da gamba family. It occupies the bass range and is the lowest instrument in the family. Similar to (but smaller than) a cello. 

contrabass

noun
  • The part or section one octave lower than bass. 

  • Any of the several contrabass instruments. 

  • The person or instrument performing the contrabass part. 

  • Double bass; string bass. 

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