Article associated with more complex proposition (7)
I believe the answer is:
theorem
'proposition' is the definition.
(theorem is a kind of proposition)
'article associated with more complex' is the wordplay.
'article' becomes 'the' (the 'definite article' part of speech).
'associated with' is a charade indicator (letters next to each other).
'complex' is an anagram indicator.
'more' is an anagram of 'orem'.
'the'+'orem'='THEOREM'
(Other definitions for theorem that I've seen before include "speculation" , "The more it changed to a proposition to be proved" , "Geometrical proposition to be proved" , "Deduced formula" , "Mathematical statement to be proved" .)