Being stupid, needs revision (5)
I believe the answer is:
dense
'being stupid' is the definition.
('dense' can be similar in meaning to 'stupid')
'needs revision' is the wordplay.
'revision' indicates an anagram.
'needs' anagrammed gives 'DENSE'.
(Other definitions for dense that I've seen before include "Closely crowded together" , "Obtuse - impenetrable" , "Close-knit" , "Slow-witted" , "Thick, compact or crowded" .)