Loathsome defendant admitting murder finally (8)
I believe the answer is:
accursed
'loathsome' is the definition.
(both can mean hated)
'defendant admitting murder finally' is the wordplay.
'defendant' becomes 'accused' (synonyms).
'admitting' means one lot of letters goes inside another (admit can mean to welcome in or accept).
'finally' indicates one should take the final letters.
The last letter of 'murder' is 'r'.
'accused' enclosing 'r' is 'ACCURSED'.
(Other definitions for accursed that I've seen before include "Wretched" , "Damned" , "Goddamn" , "Cue cards (anag) - doomed" , "Detestable (colloq.)" .)