Notorious Roman emperor (4)
I believe the answer is:
nero
'notorious roman emperor' is the definition.
(I've seen this before)
This is the entire clue.
(Other definitions for nero that I've seen before include "Roman tyrant" , "Emperor (who fiddled while Rome burned?) d. AD68" , "Roman emperor, d. AD68" , "Roman 9" , "Emperor who played the fiddle" .)