Definitions for vigilantism
Random House Webster's College Dictionary
vig•i•lan•teˌvɪdʒ əˈlæn ti(n.)(pl.)-tes.
a member of a vigilance committee.
Category: Government, Law
any person who assumes the authority of the law, as by avenging a crime.
Origin of vigilante:
1825–35;< Sp: vigilant
the actions of a vigilance committee in trying to enforce the laws
the activities of a vigilante