The word for ‘stupid’ in French is ‘stupide’. This term is used in much the same way as it is in English, to describe someone who lacks intelligence or makes poor decisions.
In addition to ‘stupide’, there are other words in French that can convey a similar meaning, depending on the context. For example, you might hear ‘bête’, which can also mean foolish or silly. The choice of words can depend on the tone you wish to convey, whether it’s more gentle or more harsh.
When using these terms, it’s important to be mindful of the cultural context and the feelings of others, just as you would in English. A word may carry different connotations based on how and where it is used, so always consider the setting in which you’re speaking.