Compurgation

Compurgation, also called wager of law and oath-helping, was a defence used primarily in medieval law. A defendant could establish his innocence or nonliability by taking an oath and by getting a required number of persons, typically twelve, to swear they believed the defendant's oath. From Latin, com = with, purgare = make clean, cleanse, excuse. Latin com is also an intensifier and turns a word into the superlative form, so compurgation, by etymology, means 'to thoroughly clean or excuse'.