smart的反义词可以是stupid或者foolish。
stupid解析如下：
一、单词读音
英式：/ˈstjuː.pɪd/
美式：/ˈstuː.pɪd/
二、单词释义
adj.愚蠢的，笨的
三、词形变化
比较级：more stupid
最高级：most stupid
四、词语搭配
act stupid: 表现得愚蠢
stupid mistake: 愚蠢的错误
stupid idea: 愚蠢的主意
look stupid: 看起来愚蠢
stupidly funny: 愚蠢得好笑
五、单词用法
stupid用以形容人或行为笨蠢，例如：That was a stupid thing to do.那样做真是愚蠢。
stupid可以用来强调自己不喜欢或不赞同某事，例如：I think it's stupid to spend all your money on clothes.我觉得把所有的钱都花在衣服上真是愚蠢。
六、双语例句
He was stupid enough to leave the car unlocked.他够傻的，车都没锁。
It was a stupid mistake and I regret it.那是一个愚蠢的错误，我后悔了。
I feel stupid asking you such a simple question.我觉得自己问你这么简单的问题很傻。
Don't be stupid, she's not interested in you.别傻了，她对你没兴趣。
A stupid person is a problem for himself, but a clever person is a problem for everyone else.愚蠢的人对自己是个问题，聪明的人对所有人都是个问题。
foolish解析如下：
一、单词读音
英式发音：ˈfuːlɪʃ
美式发音：ˈfuːlɪʃ
二、单词释义
adj.愚蠢的，愚笨的，无知的
三、词形变化
副词形式：foolishly
名词形式：foolishness
四、词语搭配
foolish mistake - 愚蠢的错误
foolish behavior - 愚蠢的行为
look foolish - 显得愚蠢
foolishly believe - 愚蠢地相信
make oneself foolish - 使自己显得愚蠢
五、单词用法
foolish可以修饰名词或名词短语。例如：Don't waste your money on foolish purchases.不要把钱浪费在愚蠢的消费上。
foolish作为形容词，用于描述人或行为，表示愚蠢、愚笨或无知。例如：She felt foolish after realizing her mistake.意识到自己的错误后，她觉得自己很愚蠢。
六、双语例句
They all jeer at the foolish speaker.
他们都嘲笑那个愚蠢的演说者。
It's foolish to idle away one's precious time.
把大好时光浪费掉是愚蠢的。
He could not account for his foolish mistake.
他无法解释他所犯的荒谬的错误。
Don't be foolish and risk your safety for a thrill.
不要愚蠢地为了刺激而冒险，保护自己的安全。
If fifty million people say a foolish thing, it is still a foolish thing.
假使五千万人讲出一件荒谬的事，那仍然是荒谬的事。