cojuror vs compurgator

cojuror

noun
  • One of a group of people who swear an oath together 

compurgator

noun
  • A character witness in canon law who swore an oath that the accused was innocent. 

  • An ‘oath-helper’ in Anglo-Saxon or Germanic law who testified to the character of an accused person. 

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