The most common and most likely answer to this crossword clue is the 9 letter word IMBECILES
I've seen this crossword clue in Independent
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More clues leading to the result IMBECILES
Buddy explains!
The straight part
We know that "Those who are stupid" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case those who are stupid = imbeciles.The cryptic/wordplay part
In cryptic crossword there's often an wordplay/cryptic part as well.This part involves a more complex hint, such as an anagram, homophone, hidden word, etc.
Sadly, We don't have an explanation for this specific crossword clue yet.
What does IMBECILES mean?
IMBECILES noun- A person with limited mental capacity who can perform tasks and think only like a young child, in medical circles meaning a person who lacks the capacity to develop beyond the mental age of a normal five to seven-year-old child.
- A fool, an idiot.