Massacre

The killing of a considerable number of human beings under circumstances of atrocity or cruelty, or contrary to the usages of civilized people; as, the massacre on St. Bartholomew's Day.

Murder.

To kill in considerable numbers where much resistance can not be made; to kill with indiscriminate violence, without necessity, and contrary to the usages of nations; to butcher; to slaughter; -- limited to the killing of human beings.