Definition of vigilantism in US English:

vigilantism

noun

  • Law enforcement undertaken without legal authority by a self-appointed group of people.

    ‘the message here is not to encourage vigilantism’
    • ‘From the moment of the judge's admonition, the nature of vigilantism in Montana changed.’
    • ‘He plays the part of a sheriff who crosses the line from law enforcement to vigilantism.’
    • ‘As he explains, vigilantism could often be considered a socially conservative form of violence.’
    • ‘He says criminologists note the ease with which public hysteria can turn into vigilantism.’
    • ‘I don't believe in vigilantism or the violation of anybody's rights.’

Origin

1930s: from vigilante + -ism.

Pronunciation

vigilantism

/ˌvijəˈlan(t)(ē)ˌizəm//ˌvɪdʒəˈlæn(t)(i)ˌɪzəm/