Undeceivable is a word that means something cannot be tricked or fooled. There are several synonyms for undecivable such as infallible, trustworthy, and dependable. Infallible refers to the quality of being incapable of making a mistake or being wrong. Trustworthy means someone or something that can be relied on, while dependable refers to the quality of being reliable and trustworthy. The terms impervious and unassailable can also be used, as both denote an object that cannot be attacked or conquered by any means. In conclusion, choosing the right synonym for undecivable depends on the context in which the word is used.