Our English newspapers began using this word, vigilante, during the last few weeks. The Prime Minister's speech denouncing theself-proclaimed Go-Rakshaks (protectors of cows) was reported on August 8, 2016 I asked some acquaintances if they its meaning. Most did not. Some made a guess, mostly not correct.
The online dictionaries say:
(noun) any person who takes the law into his or her own hands, as by avenging a crime.
(adjective) done violently and summarily, without recourse to lawful procedures