Infamous emperor (4)
I believe the answer is:
nero
'infamous emperor' is the definition.
(I've seen this in another clue)
This is the entire clue.
(Other definitions for nero that I've seen before include "Roman Emperor, 54-68 AD" , "Roman emperor infamous for his cruelty" , "Emperor, 'burnt' Rome" , "Roman 9" , "He's reputed to have fiddled while Rome burned" .)