noun (n)

• the process of paying close and continuous attention(noun.cognition)

  Example:
  Vigilance is especially susceptible to fatigue.
  

  Synonym:
  alertness, wakefulness, watchfulness
  

  source: wordnet30
• vigilant attentiveness(noun.attribute)

  Synonym:
  watchfulness, weather eye
  

  source: wordnet30
• The quality or state of being vigilant; forbearance of sleep; wakefulness.(noun)

  source: webster1913