The word "un-doubting" refers to a state of complete certainty and lack of doubt. Antonyms, or opposite words, to describe doubtfulness or skepticism include hesitant, unsure, uncertain, doubtful, and suspicious. When someone is hesitant, they are unsure and may not make decisions easily. "Unsure" or "uncertain" means that someone may not have a firm opinion or belief. Doubtful implies that someone has reservations or skepticism, while suspicious suggests a lack of trust or belief in something or someone. All of these words are antonyms of "un-doubting" as they express a lack of complete certainty and emphasize skepticism or hesitation.