When it comes to describing a "fatuous idea" - an idea that is foolish, ridiculous, and lacking in wisdom - there are a number of synonyms that can be used. For instance, you might refer to such an idea as absurd, preposterous, asinine, or naive. Alternatively, it could be described as daft, dopey, misguided, or ill-conceived. Other terms that can be used include foolish, nonsensical, irrational, or downright idiotic. Whatever word you choose to describe a "fatuous idea," it's clear that it is something that should be avoided at all costs, as it has no hope of ever succeeding or making sense.