Fustiest refers to something that is old-fashioned, outdated, and stale. There are a few synonyms for this word including dusty, musty, antiquated, passe, archaic, obsolete, and outmoded. Another word that can be used to describe this kind of thing is fusty, which has similar connotations to fustiest. Other related expressions could include dated, stale, moth-eaten, decrepit, and ancient. The use of fustiest or any of these synonyms can be used to describe something that is out of step with current tastes or standards. These words can be used to describe everything from old clothing, to furniture, to ideas.