Habituated (6)
I believe the answer is:
inured
'habituated' is the definition.
(inuring is a kind of habituating)
This is all the clue.
(Other definitions for inured that I've seen before include "Accustomed to hardship" , "Toughened through exposure" , "Hardened, perhaps ruined" , "Hardened, maybe ruined" , "Hardened against, emotion say" .)