Slaughter embraced by fanaticism as sacred (8)
I believe the answer is:
massacre
'slaughter' is the definition.
('massacre' can be a synonym of 'slaughter')
'embraced by fanaticism as sacred' is the wordplay.
'embraced' indicates a hidden word.
'MASSACRE' is hidden in the letters of 'by fanaticism as sacred'.
(Other definitions for massacre that I've seen before include "Inflict a heavy defeat" , "Indiscriminate slaughter" , "bloody victory" , "Brutal slaughter" , "Yours and mine" .)