1. A self-appointed group of people who try to prevent crime and disorder in a community where law enforcement is nonexistent, imperfect, or has broken down: When the robber shot and killed the woman who was working in the bank, hunters, who were nearby, became vigilantes and demanded that the killer put down his weapon and surrender and when he started to shoot at them, they returned fire and he died of the wounds inflicted on him.

In the past, some vigilantes went too far and executed some suspects without any valid proof of their guilt.

2. Etymology: from Spanish, "watchman, vigilante"; from Latin vigilans, vigilant-; present participle of vigilare, "to be watchful"; from vigil, "watchful".