A senatorship arranged for classical writer (12)
I believe the answer is:
'for classical writer' is the definition.
(I've seen this before)
'a senatorship arranged' is the wordplay.
'arranged' is an anagram indicator.
'senatorship' with letters rearranged gives 'ristophanes'.
(Other definitions for aristophanes that I've seen before include "Classical writer" , "Playwright" , "Greek comic dramatist - writer of Lysistrata, d. about 385 BC" , "Ancient Greek dramatist" , "Old dramatist" .)