vig ‧ i ‧ lan ‧ te /ˌvɪdʒəˈlænti, ˌvɪdʒɪˈlænti/ BrE AmE noun [countable]
[ Date: 1800-1900 ; Language: Spanish ; Origin: 'person who keeps watch, guard' , from Latin vigilans ; ⇨ ↑ vigilant ]
someone who illegally punishes criminals and tries to prevent crime, usually because they think the police are not doing this effectively
—vigilantism noun [uncountable]