Stupid, as I figure (7)
I believe the answer is:
asinine
'stupid' is the definition.
(thesaurus)
'as i figure' is the wordplay.
'figure' becomes 'nine' (I've seen this in other clues).
'as'+'i'+'nine'='ASININE'
(Other definitions for asinine that I've seen before include "Donkey-like" , "Daft" , "Is inane to be foolish" , "'Mindless, vacuous (7)'" , "Idiotic" .)