Fifth-century warrior (3)
I believe the answer is:
hun
'fifth-century warrior' is the definition.
(I've seen this in another clue)
This is all the clue.
(Other definitions for hun that I've seen before include "Warlike nomad" , "Barbarian" , "One of fourth to fifth century invaders of Europe" , "Warlike invader" , "Eg, Attila" .)