internecine

Meanings

1. Mutually destructive; most often applied to warfare.
2. Characterized by struggle within a group, usually applied to an ethnic or familial relationship.

Etymology

Borrowed from Latin internecīnus (“deadly”), from internecium (“a massacre, bloodbath; an eradication”) + -īnus. In Latin, the sememe 'between' was here not expressed by the prefix, it instead either had a somewhat emphatic meaning or meant "down, under", comparable to its use in other Latin terms related to death: see interficiō and intereō. The English current sense is thus a reanalysis of the Latin through English inter-.