Etymology
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vigilant (adj.)

late 15c., from French vigilant or directly from Latin vigilantem (nominative vigilans) "watchful, anxious, careful," present participle of vigilare "to watch, keep awake, not to sleep, be watchful," from vigil "watchful, awake" (from PIE root *weg- "to be strong, be lively"). Related: Vigilantly.

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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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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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lidless (adj.)
1520s, from lid in the "eyelid" sense + -less; usually poetic, "sleepless, ever-vigilant," as if incapable of closing the eyes.
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containment (n.)

1650s, "action or fact of containing," from contain + -ment. As the word for an international policy of the West against the Soviet Union, it is recorded from 1947, associated with U.S. diplomat George F. Kennan, who in a "Foreign Affairs" article that year advising a policy of "a long-term, patient but firm and vigilant containment of Russian expansive tendencies."

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aware (adj.)

late Old English gewær "watchful, vigilant," from Proto-Germanic *ga-waraz (source also of Old Saxon giwar, Middle Dutch gheware, Old High German giwar, German gewahr), from *ga-, intensive prefix, + *waraz "wary, cautious," from PIE root *wer- (3) "perceive, watch out for."

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Argus 
hundred-eyed giant of Greek mythology, late 14c., from Latin, from Greek Argos, literally "the bright one," from argos "shining, bright" (from PIE root *arg- "to shine; white"). His epithet was Panoptes "all-eyes." After his death, Hera transferred his eyes to the peacock's tail. Used in figurative sense of "very vigilant person."
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outlook (n.)

"mental view or survey," 1742, from out- + look (v.). The meaning "prospect for the future" is attested from 1851. Earliest sense was "a place from which an observer looks out or watches anything" (1660s). The literal sense of "vigilant watch, act or practice of looking out" (1815) is rare; look-out being used instead for this.

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alert (adv.)

"on the watch," 1610s, from French alerte "vigilant" (17c.), from prepositional phrase à l'erte "on the watch," from Italian all'erta "to the height." Second element from erta "lookout, high tower," noun use of fem. of erto, past participle of ergere "raise up," from Latin erigere "raise" (see erect (adj.)).

The adjective is attested from 1712; the noun is from 1796 as "attitude of vigilance" (as in on the alert); 1803 as "a warning report." The verb is by 1864. Related: Alerted; alerting.

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watch (v.)
Old English wæccan "keep watch, be awake," from Proto-Germanic *wakjan, from PIE root *weg- "to be strong, be lively." Essentially the same word as Old English wacian "be or remain awake" (see wake (v.)); perhaps a Northumbrian form of it. Meaning "be vigilant" is from c. 1200. That of "to guard (someone or some place), stand guard" is late 14c. Sense of "to observe, keep under observance" is mid-15c. Related: Watched; watching.
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