Fusty probably derives from the Middle English word foist, meaning "wine cask," which in turn traces to the Medieval Latin word fustis, meaning "tree trunk" or "wood." So how did fusty end up meaning "old-fashioned"? Originally, it described wine that had gotten stale from sitting in the cask for too long; fusty literally meant that the wine had the "taste of the cask." Eventually any stale food, especially damp or moldy food, was called "fusty." Those damp and moldy connotations were later applied to musty places, and later still to anything that had lost its freshness and interest—that is, to anything old-fashioned.