Confirmingly is a word that is rarely used in written or spoken English. However, there are several synonyms that can be used instead of confirmingly to convey a similar meaning. These include affirmatively, positively, definitely, conclusively, decisively, resolutely, certainly, unambiguously, unequivocally, and incontrovertibly. All of these words indicate a strong sense of certainty and confidence in the information being presented. Depending on the context of the sentence, one of these words may be a better fit for a writer or speaker's intended meaning. Overall, there are many synonyms for confirmingly that can enhance the clarity and precision of written and spoken communication.