Architectural feature on Odeon I'm converting (5,4)
I believe the answer is:
onion dome
'architectural feature' is the definition.
(I've seen this before)
'on odeon i'm converting' is the wordplay.
'converting' is an anagram indicator.
'odeon'+'im'='odeonim'
'odeonim' anagrammed gives 'iondome'.
'on'+'iondome'='ONION DOME'
(Other definitions for onion dome that I've seen before include "part of Russian church?" , "Roof shaped like a pungent vegetable, on a Russian church, perhaps" , "exotic church feature" , "Architectural feature" , "Byzantine structure?" .)