The idea of a barbarian having a companion (5)
I believe the answer is:
hunch
'the idea' is the definition.
(hunch is a kind of idea)
'barbarian having a companion' is the wordplay.
'barbarian' becomes 'hun' (as in Atilla the Hun).
'having' means one lot of letters go next to another.
'a companion' becomes 'ch' (Companion of Honour).
'hun'+'ch'='HUNCH'
'of a' is the link.
(Other definitions for hunch that I've seen before include "Intuition, suspicion" , "Lump - intuitive feeling" , "Intuitive guess" , "Bend over" , "Premonition; hump" .)