vig·i·lance \ˈvijələn(t)s\noun (-s) Etymology: Middle French, from Latin vigilantia wakefulness, vigilance, from vigilant-, vigilans + -ia -y 1.: the quality or state of being vigilant : watchfulness in respect of danger or hazard < constant vigilance against the spread of disease > 2.: readiness or alertness especially to respond to stimuli < the vigilance of a person's nerves >