Needs reform, being stupid (5)
I believe the answer is:
dense
'being stupid' is the definition.
('dense' can be similar in meaning to 'stupid')
'needs reform' is the wordplay.
'reform' indicates an anagram (letters in a new form).
'needs' is an anagram of 'DENSE'.
(Other definitions for dense that I've seen before include "Close-knit" , "Not very bright" , "Close-packed" , "Thick and tightly-packed" , "Thick; stupid" .)