compurgator
Someone who vouches for another person's innocence, trustworthiness etc. — A character witness in canon law who swore an oath that the accused was innocent.
historical
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.
Someone who vouches for another person's innocence, trustworthiness etc. — An ‘oath-helper’ in Anglo-Saxon or Germanic law who testified to the character of an accused person.
historical
Where it comes from
From Medieval Latin compurgator or Middle French compurgateur, from Latin compurgō (“to purify”).
Adapted from the Wiktionary entry compurgator (CC BY-SA 4.0).