More fatuous, exclusive clothing article (6)
I believe the answer is:
inaner
'more fatuous' is the definition.
('inane' can be a synonym of 'fatuous')
'exclusive clothing article' is the wordplay.
'exclusive' becomes 'inner' (I've seen this before).
'clothing' means one lot of letters goes inside another (some letters cover up or clothe others).
'article' becomes 'a' (the indefinite article in English).
'inner' going around 'a' is 'INANER'.
(Other definitions for inaner that I've seen before include "More stupid" , "More empty" , "More vacuous" , "Rather silly" , "What's relatively lemon-like" .)