StupidityI think that it's fine to have a definition for "stupid", but in day to day usage "stupid" covers a very broad range of human activity.
I have a relative (now dead) who couldn't read, but was otherwise quite competent. Ignorant only of the written word.
Thirty odd years ago I worked in a hospital for "crippled" children. My favorite kid had Cerebral palsy. Ignorant? Stupid? No, he was too happy and sweet to be called anything like that.
I have visual Dyslexia. Reading and writing was a major problem for me. Around 10 or 11 I started to use a mental shorthand to speed up the writing process for long writing assignments in school. Rather than writing out each word and trying to spell it right, I wrote only the first letter of the word
(for some reason I NEVER transpose the first letter). After the report was written, I only had to recall the first word to write out the entire report. Unfortunately, I then had to compare the
appearance of each word to the appearance of that word in a dictionary.
Needless to say, I didn't enjoy reading. At that time, I timed myself reading from the top of one page to the bottom of the back of that page.
Ten minutes. I kid you not.
Rather than trying to read
each letter of each word, I turned the book upside down, and taught myself to read the ENTIRE word. It worked.
Although I will still make mistakes writing/typing, I can now
read rapidly through
word pattern recognition. Both right side up or upside down.

To me, stupid/stupidity is harder to define than reading what's in the dictionary.
I've known very intelligent people to do stupid things.
I've meet relatively uneducated people that were smarter than the average person.
In the end, I'll go along with this - to paraphrase the US Supreme Court's Justice Stewart -
I can’t define it, but I know it when I see it.
End note - Wikipedia has an example of how a visual dyslexic
sees the word
teapot.
