internecine

 
Pronunciation: /ˌɪntəˈniːsʌɪn/

adjective

  • destructive to both sides in a conflict: the region’s history of savage internecine warfare
  • relating to conflict within a group: the party shrank from the trauma of more internecine strife

Origin:

mid 17th century (in the sense 'deadly, characterized by great slaughter'): from Latin internecinus, based on inter- 'among' + necare 'to kill'