the fact of being stupid, or a stupid action, idea, etc.

She said that the idea was folly. 她说这是个愚蠢的主意。

[ + to infinitive ] It would be folly for the country to become involved in the war. 那个国家要是参战的话实属愚蠢之举。

a building in the form of a small castle, temple, etc., that has been built as a decoration in a large garden or park

a Gothic garden folly 一个歌特式的花园建筑