Stupid article fiancee regularly defends (5)
I believe the answer is:
inane
'stupid' is the definition.
(I've seen this before)
'article fiancee regularly defends' is the wordplay.
'article' becomes 'an' (indefinite article).
'regularly' indicates alternate letters (regularly take one letter, leave next etc.).
'defends' indicates putting letters inside (inserted letters are held or defended).
The alternating letters of 'fiancee' are 'ine'.
'an' going inside 'ine' is 'INANE'.
(Other definitions for inane that I've seen before include "Delirious" , "Moronic" , "Idiotic" , "Frivolous" , "Fatuous, mindless" .)