This is not from a crossword but it is a word puzzle and I know there's a lot of very clever people on this forum. Besides, you might like the challenge!
The requirement is to identify three words.
All the words are adjectives.
All the words mean more or less the same thing.
The first word has 9 letters.
The second word has 10 letters.
The third word has 11 letters.
There is a clue: If you are not too clever, this could a distinct advantage on this puzzle!
I have the first word, which is DIMWITTED.
There are additional stipulations. I'm not sure if they help you find the words but they do confirm when you have the correct word.
The 9 letter word may be split 3 different ways:-
3+6 = DIM + WITTED
6+3 = WITTED + TED
3+3+3 = DIM + WIT + TED
All words will be found in www.dictionary.com.
The 10 letter word may be split in 2 different ways:-
5+2+3, 5+3+2.
The 11 letter word may be split in 8 different ways:-
2+2+3+2+2, 2+3+2+2+2, 2+3+3+3, 2+3+4+2, 2+3+6, 4+3+2+2, 4+5+2 and 4+7.
Over to you....