compurgator

noun3

1. •
   Someone who vouches for another person's innocence, trustworthiness etc.
2. •
   (historical) A character witness in canon law who swore an oath that the accused was innocent.

   • If a wise woman fell under suspicion from the authorities her neighbours might rally to her defence, providing compurgators in court, or drawing up certificates testifying to her innocence. — 1971
3. •
   (historical) An ‘oath-helper’ in Anglo-Saxon or Germanic law who testified to the character of an accused person.