/in'teuhr nee"seen, -suyn, -nes"een, -nes"uyn/ , adj.
1. of or pertaining to conflict or struggle within a group: an internecine feud among proxy holders.
2. mutually destructive.
3. characterized by great slaughter; deadly.
Also, internecive /in'ter nee"siv, -nes"iv/ .
[ 1655-65; internecinus, internecivus murderous, equiv. to internec ( are ) to kill out, exterminate ( inter- INTER- + necare to kill) + -inus -INE 1 , -ivus -IVE ]