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' indicates a hidden word.
'NERO' can be found hidden inside '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" .)