FOLLY

(STUPIDITY) [noun] - stupidity, or a stupid action, idea, etc.She said that the idea was folly. [U]It would be folly for the country to become involved in the war. [U + to infinitive]Customers were furious to discover that they had subsidized the bank's follies in investing funds overseas. [C]His latest folly was buying a second-hand car which turned out to have a faulty engine. [C]