Stupid means showing no thought at all. Putting petrol in a diesel car, texting while crossing the road, sending the angry email at midnight.
Be careful where you point it. Calling an idea, a rule or a mistake stupid is ordinary English; calling a person stupid is an insult, and it lands harder than the polite equivalents do in many other languages, with silly, daft and foolish all much softer. Stupid also works as pure irritation aimed at objects: this stupid printer, that stupid door. The noun is stupidity, the verb in the family is stupefy, and stupidly at the front of a sentence is an apology, as in stupidly, I left the passport at home. The safe move is to say the mistake was stupid rather than that the person is.
1adjectivestupidOf a person: slow to understand; lacking intelligence.~86%
“He is not stupid, he simply was not listening.”
2adjectiveactionOf an action, idea or mistake: badly thought out.~12%
“Leaving the window open was a stupid mistake.”
3adjectiveshowUsed to show annoyance with a thing. Informal.~2%
“This stupid lid will not come off.”
informal in this meaning — an editor’s judgement
Shares are an estimate: a language model read 8 sentences found in the wild and placed 8 of them on a sense — a count of our sample, not a measurement of English.
Also accepted in games: dumb
Latin stupidus did not mean unintelligent. It meant struck senseless, amazed, and came from stupeō, to be stunned or struck senseless. Behind that lies a Proto-Indo-European root meaning to push or hit, the same one that gives English stop. So the original stupid person is not the one who cannot think, but the one who has been hit so hard they cannot think for a moment, which is the sense still alive in stupefied.
Proto-Indo-European
*(s)tewp-
Latin
stupidus
Middle French
stupide
English, today
stupid
Built from
From Middle French stupide, from Latin stupidus. From Middle French stupide, from Latin stupidus (“struck senseless, amazed”), from stupeō (“be amazed or confounded, be struck senseless”), from Proto-Indo-European (s)tup-, (s)tewp- (“to push, stick”), from Proto-Indo-European (s)tew- (“to push, hit”). Cognate with Old High German stubarōn (“to be astonished, be stunned, be blocked”). Related also to Old English stoppian (“to block, stop”). More at stop.
Etymology from Wiktionary, CC BY-SA