Proposition of article has Rome shocked (7)
I believe the answer is:
theorem
'proposition' is the definition.
(theorem is a kind of proposition)
'article has rome shocked' is the wordplay.
'article' becomes 'the' (the 'definite article' part of speech).
'has' says to put letters next to each other.
'shocked' indicates an anagram.
'rome' anagrammed gives 'orem'.
'the'+'orem'='THEOREM'
'of' is the link.
(Other definitions for theorem that I've seen before include "Statement to be proved in maths" , "(Maths) proposition" , "Proved mathematical hypothesis" , "Proven hypothesis" , "Geometrical proposition to be proved" .)