a person who is not very bright
"The economy, stupid!"
A stupid person; a fool.
"He made such a stupid mistake that everyone laughed at him."
lacking or marked by lack of intellectual acuity
"His stupid argument ignored all the facts we had discussed earlier."
Lacking in intelligence or exhibiting the quality of having been done by someone lacking in intelligence.
"The instructions for assembling that flat-pack shelf were so stupidly confusing that I ended up building a ladder instead of a table."
In plain English: Stupid means lacking good sense or common knowledge.
"The stupid traffic jam made me late for work."
Usage: Use stupid to describe either an unintelligent person or something foolishly made, though it is often considered harsher than synonyms like silly. Avoid using this term when you mean merely difficult or complex, as those situations require words like confusing instead.
Extremely.
"I couldn't believe how stupidly fast he drove down that narrow alleyway."
"He stared stupidly at the locked door for hours."
The word "stupid" comes from the Latin stupere, meaning to be amazed or struck senseless. It entered Middle French as stupide before traveling into English with this original sense of being stunned.