Final answer:
The word 'internecine' refers to conflicts or struggles that are destructive to both sides involved, suggesting violent and deadly battles that result in heavy casualties.
Step-by-step explanation:
The meaning of the word 'internecine' is most accurately captured by option 2, which is marked by slaughter. Historically, the term has been used to describe conflicts or struggles that are extremely destructive to both sides involved, often within a group or organization. The word 'internecine' conveys a sense of deep-rooted, often mutual destruction that usually implies violent conflict or battles resulting in heavy casualties.