Stupidity means "no brain", "lack of common sense" and "lack of judgment". It is foolish to fight with his neighbor. It is foolish of him to miss such an opportunity. He was so stupid that he missed such an opportunity. It is foolish of you to say so. Stupid means "retarded" and "slow to respond". Mary made a stupid mistake. Mary made a stupid mistake. He is stupid in math. He is stupid in math. Henry is too stupid to understand such a complicated problem. Henry is too stupid to understand such a complicated problem. Silly means "simple-minded, ignorant" and "stupid". For example, don't be stupid! Don't be silly! Stop asking such stupid questions! Stop asking such stupid questions! It's foolish of you to believe him. You believe that he is stupid. Stupidity is sometimes emotional. You silly child. You silly child. To sum up, idiot is equivalent to "stupidity" in Chinese, stupidity is equivalent to "stupidity" and stupidity is equivalent to "stupidity". Besides, we will also use the word fool. Fool is a noun, meaning "fool" (often referring to people with congenital mental retardation). For example, don't act like a fool. Don't be silly.