The Collaborative International Dictionary of English v.0.48:

Vigil \Vig"il\, n. [OE. vigile, L. vigilia, from vigil awake,
   watchful, probably akin to E. wake: cf. F. vigile. See
   Wake, v. i., and cf. Reveille, Surveillance, Vedette,
   Vegetable, Vigor.]
   1. Abstinence from sleep, whether at a time when sleep is
      customary or not; the act of keeping awake, or the state
      of being awake; sleeplessness; wakefulness; watch. "Worn
      out by the labors and vigils of many months." --Macaulay.
      [1913 Webster]

            Nothing wears out a fine face like the vigils of the
            card table and those cutting passions which attend
            them.                                 --Addison.
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   2. Hence, devotional watching; waking for prayer, or other
      religious exercises.
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            So they in heaven their odes and vigils tuned.
                                                  --Milton.
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            Be sober and keep vigil,
            The Judge is at the gate.             --Neale
                                                  (Rhythm of St.
                                                  Bernard).
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   3. (Eccl.)
      (a) Originally, the watch kept on the night before a
          feast.
      (b) Later, the day and the night preceding a feast.
          [1913 Webster]

                He that shall live this day, and see old age,
                Will yearly on the vigil feast his neighbors,
                And say, "To-morrow is St. Crispian." --Shak.
          [1913 Webster]
      (c) A religious service performed in the evening preceding
          a feast.
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   Vigils of flowers or Watchings of flowers (Bot.), a
      peculiar faculty belonging to the flowers of certain
      plants of opening and closing their petals at certain
      hours of the day. [R.]
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WordNet (r) 3.0 (2006):

vigil
    n 1: a period of sleeplessness
    2: the rite of staying awake for devotional purposes (especially
       on the eve of a religious festival) [syn: vigil, watch]
    3: a purposeful surveillance to guard or observe [syn: watch,
       vigil]

Moby Thesaurus II by Grady Ward, 1.0:

81 Moby Thesaurus words for "vigil":
   Mass, alertness, all-night vigil, bedtime prayer, camp meeting,
   church, church service, compline, consciousness, custodianship,
   custody, devotions, divine service, duty, eagle eye,
   evening devotions, evensong, exercises, guard, guardedness,
   guardianship, insomnia, insomniac, insomnolence, insomnolency,
   invigilation, lauds, lidless vigil, liturgy, lookout, matins,
   meeting, monitoring, morning devotions, night song, none, nones,
   novena, observance, office, peeled eye, praise meeting, prayer,
   prayer meeting, prayers, prime, prime song, proctoring, prudence,
   public worship, qui vive, restlessness, revival, revival meeting,
   sentience, service, sext, sharp eye, sleeplessness, stewardship,
   surveillance, tent meeting, tierce, tossing and turning, undersong,
   vesper, vespers, vigilance, vigils, wake, wakefulness, wariness,
   watch, watch and ward, watch meeting, watch night,
   watch-night service, watchful eye, watchfulness, watching,
   weather eye