Savage slurs they endlessly spread (8)
I believe the answer is:
ruthless
'savage' is the definition.
(thesaurus)
'slurs they endlessly spread' is the wordplay.
'endlessly' means to remove the last letter.
'spread' indicates anagramming the letters.
'slurs'+'they'='slursthey'
'slursthey' with its last letter removed is 'slursthe'.
'slursthe' with letters rearranged gives 'RUTHLESS'.
(Other definitions for ruthless that I've seen before include "Showing no mercy" , "Without pity, merciless" , "Unmerciful" , "Harsh" , "Lacking pity or mercy" .)