A vigil, from the Latin vigilia meaning wakefulness (Greek: pannychis, παννυχίς or agrypnia ἀγρυπνία), is a period of purposeful sleeplessness, an occasion for devotional watching, or an observance. The Italian word vigilia has become generalized in this sense and means "eve" (as in on the eve of the war).
Eves of religious celebrations 
A vigil may be held on the eve of a religious festival (feast days), observed by remaining awake—"watchful"—as a devotional exercise or ritual observance on the eve of a holy day. Such liturgical vigils usually consist of psalms, prayers and hymns, possibly a sermon or readings from the Holy Fathers, and sometimes periods of silent meditation.
The term "morning" means that the observance begins on the evening before. In traditional Christianity, the celebration of liturgical feasts begins on the evening before the holy day because the Early Church continued the Jewish practice of beginning the day at sunset rather than midnight.
Most likely the best known vigil is the Easter Vigil held on Holy Saturday. The Midnight Mass held on Christmas Eve is a remnant of this practice. Christmas Eve is a time of reflection for Christians in the U.S. and all over the world.
In the Eastern Orthodox Church an All-Night Vigil (consisting of Great Vespers, Matins and the First Hour) is held on the eves of Sundays and all Major Feast Days (such as the Twelve Great Feasts and the Feast Days of important Saints) during the liturgical year.
Vigils at the time of death 
In Christianity, especially the Eastern Orthodox and Roman Catholic traditions, a vigil is often held when someone is gravely ill or mourning. Prayers are said and votives are often made. Vigils extend from eventual death to burial, ritualistically to pray for a loved one, but more so their body is never left alone.
Medieval knights 
During the Middle Ages, a squire on the night before his knighting ceremony was expected to take a cleansing bath, fast, make confession, and then hold an all-night vigil of prayer in the chapel, preparing himself in this manner for life as a knight. For the knighting ceremony, he dressed in white as a symbol for purity.
See also 
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- παννυχίς. Liddell, Henry George; Scott, Robert; A Greek–English Lexicon at Perseus Project
- ἀγρυπνία. Liddell, Henry George; Scott, Robert; A Greek–English Lexicon at Perseus Project
- Cross, F. L. Cross; Livingstone, E. A., eds. (2005). The Oxford Dictionary of the Christian Church. Oxford University Press. Available (limitedly) online at the Oxford Reference.
- Eve of a Feast, Catholic Encyclopedia