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.
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   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.
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WordNet (r) 3.0 (2006):

vigilance committee
    n 1: a volunteer committee to maintain order where an efficient
         legal system does not exist