Article more about hypothesis (7)
I believe the answer is:
theorem
'hypothesis' is the definition.
(I've seen this before)
'article more about' is the wordplay.
'article' becomes 'the' (the definite article in English).
'about' is an anagram indicator.
'more' anagrammed gives 'orem'.
'the'+'orem'='THEOREM'
(Other definitions for theorem that I've seen before include "Logical proposition" , "Mathematical axiom" , "Deduced formula" , "Demonstrable proposition" , "Mathematical formula" .)