What Does It Mean?

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From our dictionary:
in•ter•ne•cine

(in"tur-nē'sēn, -sīn, -nes'ēn, -nes'īn),
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,in•ter•ne•cive Pronunciation: (in"ter-nē'siv, -nes'iv).