felt-tip vs gladius

felt-tip

noun
  • A felt-tip pen. 

verb
  • To write with a felt-tip pen. 

gladius

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

  • A Roman sword roughly two feet long. 

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