cotter pin vs fibula

cotter pin

noun
  • A pin or wedge inserted through a slot to hold machine parts together; a cotter. 

  • A split pin, the ends of which project through an object being fastened and are bent back to hold it in place. 

fibula

noun
  • An ancient kind of brooch used to hold clothing together, similar in function to the modern safety pin. 

  • The smaller of the two bones in the lower leg. 

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