Habituated in rude usage (6)
I believe the answer is:
inured
'habituated' is the definition.
(inuring is a kind of habituating)
'in rude usage' is the wordplay.
'usage' is an anagram indicator.
'rude' anagrammed gives 'ured'.
'in'+'ured'='INURED'
(Other definitions for inured that I've seen before include "used to it" , "Hardened against, emotion say" , "Hardened against, toughened" , "Toughened through exposure" , "Accustomed to hardship" .)