Detested person or thing (8)
I believe the answer is:
anathema
I believe this clue is a double definition.
'detested person' is the first definition.
(I've seen this before)
'thing' is the second definition.
(I have seen 'hateful thing' mean 'anathema' so perhaps 'thing' could also mean 'anathema')
(Other definitions for anathema that I've seen before include "denunciation" , "Detested person or thing - excommunication" , "Curse of the Church, or detested person" , "Object of detestation" , "It's detested or abhorred" .)