1.(used with a sing. verb) Good faith; sincerity. 2.(used with a pl. verb) Information that serves to guarantee a person's good faith, standing, and reputation; authentic credentials: Sakharov's bona fides within the Soviet system . . . have given added weight to his message (Christian Science Monitor).
ETYMOLOGY:
Latin bona fids, good faith : bona, feminine of bonus, good + fids, faith.