internecine
/ˌɪntəˈniːsaɪn/adjective
1- destructive to both sides in a conflict（冲突双方）两败俱伤的：
the region's history of savage internecine warfare.
该地区野蛮相互残杀的战争史。
1.1
- of or relating to conflict within a group or organization内部斗争的。
词源
mid 17th cent. （in the sense 'deadly， characterized by great slaughter'）： from Latin internecinus, based on inter- among + necare 'to kill'.