ballpoint vs plectrum

ballpoint

noun
  • A kind of needle with a rounded tip. 

  • A ballpoint pen. 

plectrum

noun
  • A small piece of plastic, metal, ivory, etc., for plucking the strings of a guitar, lyre, mandolin, etc. 

  • A projection of bone or other stiff tissue, such as the ridges in some insects' stridulatory organs. 

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