Historic barbarian – a hard-headed French one (3)
I believe the answer is:
hun
'historic barbarian' is the definition.
'hun' can be an answer for 'barbarian' (I've seen this before). I am unsure of the 'historic' bit.
'a hard-headed french one' is the wordplay.
'a hard-headed french' becomes 'h' (I am not sure about this - if you are sure you should believe this answer much more).
'one' becomes 'un' (I've seen this in other clues).
'h'+'un'='HUN'
Can you help me to learn more?
(Other definitions for hun that I've seen before include "Eg, Attila" , "Barbarian" , "One led by Attila" , "One of fourth to fifth century invaders of Europe" , "Warlike nomad" .)