From The Collaborative International Dictionary of English v.0.48 :
Vigilance \Vig"i*lance\, n. [L. vigilantia: cf. F. vigilance.]
1. The quality or state of being vigilant; forbearance of
sleep; wakefulness.
[1913 Webster]
2. Watchfulness in respect of danger; care; caution;
circumspection. --Cowper.
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And flaming ministers to watch and tend
Their earthly charge; of these the vigilance
I dread. --Milton.
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3. Guard; watch. [Obs.] "In at this gate none pass the
vigilance here placed." --Milton.
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Vigilance committee, a volunteer committee of citizens for
the oversight and protection of any interest, esp. one
organized for the summary suppression and punishment of
crime, as when the processes of law appear inadequate.
[1913 Webster]
From WordNet (r) 2.0 :
vigilance committee
n : a volunteer committee to maintain order where an efficient
legal system does not exist