Roman conspirator (5)
I believe the answer is:
casca
'roman conspirator' is the definition.
(I've seen this in another clue)
This is all the clue.
(Other definitions for casca that I've seen before include "Stabbed by him, Caesar" , "Servilius -----, senator co-assassin of Julius Caesar" , "Roman conspirator" , "Conspirator responsible for rent" , "envious assassin" .)