Principal among the Romans (4)
I believe the answer is:
hero
'principal' is the definition.
(thesaurus)
'among the romans' is the wordplay.
'among' indicates the answer is hidden within the clue.
'HERO' is hidden in the letters of 'the romans'.
(Other definitions for hero that I've seen before include "lover whose lamp went out tragically" , "object of adulation" , "Exceptionally brave person" , "Lion" , "Man admired for courage and achievement" .)