argonaut vs freebooter

argonaut

noun
  • An adventurer on a dangerous but rewarding quest. 

  • Any of several species of shelled octopods of the family Argonautidae (of which only the genus Argonauta is not extinct). 

freebooter

noun
  • An adventurer who pillages, plunders or wages ad-hoc war on other nations. 

  • One who rehosts online media without authorization; one who freeboots. 

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