1. A period spent in doing something through the night or during a time when someone is staying awake: Mark was guarding his family from possible attacks by bears by holding a vigil when they were up in the mountains during their vacation.
2. A night-time period of staying awake to look after a sick person, to pray, etc.: As Tim's father lay in a coma, his family kept a vigil and prayed that he would recover.

Some religious vigils include prayers that take place on the eve of special holy days.