vigil

From Latin vigil 'awake, watchful' and the verb vigilāre 'to stay awake, keep watch,' built on vigēre 'to be lively, be full of energy.' Originally about staying awake at night on guard, it gave English vigilant (alert to danger), vigilance (the state of watchfulness), surveillance (via French surveiller, 'watching from above') and invigilate (to watch over an exam).