When handling claims or accusations, it is important to determine if they are unsubstantiated. Some synonyms for the word "unsubstantiated" include baseless, unfounded, unsupported, groundless, unproven, unverified, and conjectural. These words are often used to describe statements that lack evidence or proof. Using synonyms can help to avoid repetition and add interest to your writing. It is important to choose the right word to convey the necessary meaning and prevent misunderstanding. Make sure to consider the context and tone of the sentence when selecting a synonym for "unsubstantiated".