Stupid? Not this crossword (8)
I believe the answer is:
clueless
'stupid?' is the definition.
(I've seen this before)
'not this crossword' is the wordplay.
I cannot really see how this works, but
'not' could be 'less' (I've seen this in other clues) and 'less' is present in the answer.
'this' could be 'clue' (the clue referring to itself!) and 'clue' is found in the answer.
This accounts for all the letters.
This may be the basis of the clue (or it may be nonsense).
Can you help me to learn more?
(Other definitions for clueless that I've seen before include "Totally uninformed about what's going on" , "Completely at sea about what's going on" , "Without any understanding" , "such a crossword can't be solved!" , "how I started this puzzle!" .)