Complex article initially taken in in an instant (9)
I believe the answer is:
intricate
'complex' is the definition.
('intricate' can be similar in meaning to 'complex')
'article initially taken in in an instant' is the wordplay.
'article initially' becomes 'at' (I am not sure about this - if you are sure you should believe this answer much more).
'taken in' is an insertion indicator.
'an instant' becomes 'trice' ('trice' can be a synonym of 'instant').
'in'+'trice'='intrice'
'at' put within 'intrice' is 'INTRICATE'.
Can you help me to learn more?
(Other definitions for intricate that I've seen before include "puzzlingly obscure" , "puzzling" , "Complex, labyrinthine" , "Very complicated and involved" , "ornate" .)