A Roman emperor in a manner of speaking (4)
I believe the answer is:
nero
'a roman emperor' is the definition.
(Roman emperor, 37-68 AD)
'in a manner of speaking' is the wordplay.
'in' says the answer is hidden in the clue.
'NERO' is hidden within 'manner of speaking'.
(Other definitions for nero that I've seen before include "Ruler" , "Emperor (who fiddled while Rome burned?) d. AD68" , "Roman Emperor, 54-68 AD" , "Roman Emperor notorious for vice and luxury" , "He's reported to have fiddled while Rome burned" .)