Roman censor to suppress new division in poem (5)
I believe the answer is:
canto
'division in poem' is the definition.
'roman censor to suppress new' is the wordplay.
'roman censor' becomes 'cato' (Cato the Elder).
'to suppress' is an insertion indicator.
'new' becomes 'n'.
'cato' placed around 'n' is 'CANTO'.
(Other definitions for canto that I've seen before include "verse" , "piece of poetry" , "part of long poem" , "Section of a long poem" , "melodic piece of music" .)