Greco-Roman in form with Ionic and Corinthian capitals (7)
I believe the answer is:
classic
'greco-roman' is the definition.
Both the definition and answer are adjectives. Maybe you can see a link between them that I don't see?
'form with ionic and corinthian capitals' is the wordplay.
I cannot quite understand how this works, but
'form' could be 'class' (synonyms) and 'class' is present in the answer.
This explanation may well be incorrect...
'in' acts as a link.
Can you help me to learn more?
(Other definitions for classic that I've seen before include "work of the highest quality" , "Quintessential" , "Serving as a standard - of the highest quality" , "Timeless-quality work; a race" , "Accepted as excellent" .)