Stupid articles penned by fashion journalist (9)
I believe the answer is:
fatheaded
'stupid' is the definition.
('fatheaded' can be similar in meaning to 'stupid')
'articles penned by fashion journalist' is the wordplay.
'articles' becomes 'athe' (two examples of the part-of-speech: a+the).
'penned by' indicates putting letters inside.
'fashion' becomes 'fad' (fad is a kind of fashion).
'journalist' becomes 'ed' (short for editor).
'athe' placed inside 'fad' is 'fathead'.
'fathead'+'ed'='FATHEADED'
(Other definitions for fatheaded that I've seen before include "Stupid" , "weakened" , "Informally foolish with obese cranium" .)