The word "unbased" refers to something that lacks a solid foundation or justification. There are several synonyms that can be used to convey this meaning, including unfounded, baseless, groundless, unsupported, unsubstantiated, and unjustified. These words all imply a lack of evidence or reasoning to support a particular claim or idea. Other synonyms for "unbased" might include flimsy, weak, feeble, shaky, or dubious. It's important to use synonyms to add variety and clarity to your writing, and to choose the most appropriate word based on the context and tone of your message.