Sororicide

Sororicide (from Latin sororicidium; from soror 'sister' and -cīdium 'killing') is the act of murdering one's own sister. There are a number of examples of sororicide and fratricide in adolescents, even pre-adolescents, where sibling rivalry and resulting physical aggression can get out of hand and lead to the death of one of them, particularly when a potent weapon is available or one is significantly older than the other and misjudges their own strength.