Merriam-Webster Collegiate Dictionary - fratricide

 noun  Etymology: in sense 1, from Middle English, from Middle French or Latin; Middle French, from Latin fratricida, from fratr-, frater brother + -cida -cide; in sense 2, from Middle French or Latin; Middle French, from Latin fratricidium, from fratr-, frater + -cidium -cide  Date: 15th century  1. one that murders or kills his or her own brother or sister or an individual (as a countryman) having a relationship like that of a brother or sister  2. the act of a ~  • fratricidal adjective