"Unbelievably" is an adverb used to describe something that is difficult to believe or comprehend. There are several synonyms for this word which can be employed to add variety and interest to written and spoken language. The first synonym is "incredibly," which means something that is hard to believe or astonishing. Another synonym is "astoundingly," which describes something that is shockingly unexpected. Additionally, "amazingly" is a synonym that conveys a sense of wonder and surprise. Finally, "remarkably" is a synonym that suggests that something is uncommon or unusual. By using different synonyms for "unbelievably," writers and speakers can add depth and nuance to their expression.