Roguish, hard-hearted companion (4)
I believe the answer is:
arch
'roguish' is the definition.
(I've seen this before)
'hard-hearted companion' is the wordplay.
'hearted' means to look at the middle letters.
'companion' becomes 'ch' (Companion of Honour).
The central letters of 'hard' are 'ar'.
'ar'+'ch'='ARCH'
(Other definitions for arch that I've seen before include "Bend into upward curve" , "Prefix meaning cheif, perhaps enemy" , "Playfully superior" , "Mischievous - curve" , "Chief - supporter - cunning" .)