internecineyoudaoicibaDictYouDict[internecine 词源字典]
internecine: [17] Etymologically, internecine denotes ‘attended by great slaughter’. Its modern connotations of ‘conflict within a group’, which can be traced back to the 18th century (Dr Johnson in his Dictionary 1755 defines it as ‘endeavouring mutual destruction’), presumably arise from the standard interpretation of inter- as ‘among, between’. But in fact in the case of internecine it was originally used simply as an intensive prefix.

The word was borrowed from Latin internecīnus, a derivative of internecāre ‘slaughter, exterminate’. This was a compound verb formed with the intensive inter- from necāre ‘kill’ (a relative of English necromancy and pernicious).
=> necromancy, pernicious[internecine etymology, internecine origin, 英语词源]
internecine (adj.)youdaoicibaDictYouDict
1660s, "deadly, destructive," from Latin internecinus "very deadly, murderous, destructive," from internecare "kill or destroy," from inter (see inter-) + necare "kill" (see noxious). Considered in the OED as misinterpreted in Johnson's Dictionary [1755], which defined it as "endeavouring mutual destruction," on association of inter- with "mutual" when the prefix supposedly is used in this case as an intensive. From Johnson, wrongly or not, has come the main modern definition of "mutually destructive."