It seems that they have only just worked this out. Certainly lots of people are talking about it.

In my mind, the opposite of smart is stupid.

Now, I know that most of these people don’t think this. But they must be bit slow to think that I think of it in the same way as they do. Here is a definition from Wikitionary. Strangely their version of smart does not seem to form part of the English language.

smart

Definitions from Wiktionary, a free dictionary

English

Etymology

From Old English smeortan, from West Germanic *smertan, whence also Old High German smerzan.

Pronunciation

• enPR: smärt
• Audio (US)^{help, file}
• Rhymes: -ɑː(r)t

Adjective

smart (comparative smarter, superlative smartest)

1. exhibiting social ability or cleverness
2. exhibiting intellectual knowledge, such as that found in books
3. good-looking, as a smart outfit
4. cleverly humorous, in a way that is rude and disrespectful however; wise guy.

   He became tired of his daughter’s sarcasm and smart remarks.

Antonyms

• (exhibiting social ability): backward, boorish, dull, inept
• (exhibiting intellectual knowledge): ignorant, uncultivated, simple
• (good-looking): garish, outré, tacky

Synonyms

• (exhibiting social ability): bright, capable, sophisticated, witty
• (exhibiting intellectual knowledge): cultivated, educated, learned
• (good-looking): attractive, chic, stylish, handsome