Infamous Roman emperor (4)
I believe the answer is:
nero
'infamous roman emperor' is the definition.
(I've seen this in another clue)
This is all the clue.
(Other definitions for nero that I've seen before include "Matricidal emperor" , "Wicked fiddler" , "Tyrannical Roman emperor" , "Emperor, 'burnt' Rome" , "Roman tyrant" .)