Long article about a provincial Greek (7)
I believe the answer is:
achaean
'provincial greek' is the definition.
(I've seen this before)
'long article about a' is the wordplay.
'long' becomes 'ache' ('ache' can be a synonym of 'long'**).
'article' becomes 'an' (indefinite article).
'about' is an insertion indicator.
'ache'+'an'='achean'
'achean' placed around 'a' is 'ACHAEAN'.
(Other definitions for achaean that I've seen before include "Ancient Greek" , "about ancient Greeks" , "provincial Greek" .)