plectrum vs spicule

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. 

spicule

noun
  • A sharp, needle-like piece. 

  • A needle-like mating structure found only in male nematodes. 

  • A tiny glass flake formed during the manufacture of glass vials 

  • A small spike of flowers. 

  • A jet of matter ejected from the photosphere of the sun. 

  • Any of many needle-like crystalline structures that provide skeletal support in marine invertebrates like sponges. 

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