Hate to heal badly (6)
I believe the answer is:
loathe
'hate' is the definition.
(loathing is a kind of hating)
'to heal badly' is the wordplay.
'badly' indicates an anagram.
'to'+'heal'='toheal'
'toheal' is an anagram of 'LOATHE'.
(Other definitions for loathe that I've seen before include "Find repugnant" , "Abhor, execrate" , "Feel strong disgust for" , "Cordially detest, thoroughly dislike" , "Greatly hate" .)