gladius vs rachis

gladius

noun
  • A pen, a hard internal bodypart of certain cephalopods, made of chitin-like material. 

  • A Roman sword roughly two feet long. 

rachis

noun
  • An anatomical shaft or axis in a marine invertebrate. 

  • The main shaft of either a compound leaf, head of grain, or fern frond. 

  • The central shaft of a feather. 

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