Etymology
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vigilante (n.)
"member of a vigilance committee," 1856, American English, from Spanish vigilante, literally "watchman," from Latin vigilantem (nominative vigilans) "watchful, anxious, careful," from vigil "watchful, awake" (from PIE root *weg- "to be strong, be lively"). Vigilant man in same sense is attested from 1824 in a Missouri context. Vigilance committees kept informal rough order on the U.S. frontier or in other places where official authority was imperfect.
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*weg- 
Proto-Indo-European root meaning "to be strong, be lively."

It forms all or part of: awake; bewitch; bivouac; invigilate; reveille; surveillance; vedette; vegetable; velocity; vigil; vigilant; vigilante; vigor; waft; wait; wake (v.) "emerge or arise from sleep;" waken; watch; Wicca; wicked; witch.

It is the hypothetical source of/evidence for its existence is provided by: Sanskrit vajah "force, strength," vajayati "drives on;" Latin vigil "watchful, awake," vigere "be lively, thrive," velox "fast, lively," vegere "to enliven," vigor "liveliness, activity;" Old English wacan "to become awake," German wachen "to be awake," Gothic wakan "to watch."
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