What follows below is essentially a repeat of something I have posted on this board each year since 2003 (except for 2007 when I was not computer accessible!). I personally feel it is worthwhile to repeat it since it is a nice part of the Catholic tradition (hence its posting in this forum, "CATHOLICISM 101"). Some new folks come on this board each year and it doesn't hurt for previous board members either.
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Starting on December 17 the more-"proximate-preparation-for-Christmas" part of Advent starts. One of the features is that for seven evenings a particular form of antiphon, known as an "O Antiphon", is used with the Magnificat (Mary's Canticle) in Evening Prayer (Vespers) of the LITURGY OF THE HOURS.

Each one focuses on one of the titles which Christians see as Messianic. They are probably most familiar to people as the individual verses of the hymn "O Come, O Come Emmanuel".
December 17/ O Sapientia: “O Wisdom"
December 18/ O Adonai: “O Sacred Lord"
December 19/ O Radix Jesse: “O Flower of Jesse’s stem"
December 20/ O Clavis David: “O Key of David"
December 21/ O Oriens: “O Radiant Dawn"
December 22/ O Rex Gentium: “O King of all the nations"
December 23/ O Emmanuel: “O Emmanuel"

[For those who wonder why there is no late-Advent "O Antiphon" for December 24: the Christmas liturgical season already starts with Evening Prayer I (First Vespers) of Christmas on the evening of December 24! Advent is over.]

A fairly nice article on these O Antiphons by a Fr. William Saunders and originally published in the Arlington Catholic Herald is available at:
Fr. William Saunders article on the O ANTIPHONS


Edward Pothier

hey friend awesome post there i didnt know about that one bit. i will check that article when i wake up thanks for your post budddy

A little late and a dollar short, but there are, in addition to the 7 standard O antiphons post-Trent, several others that various western Churches have used. For instance, in Spain they celebrate the Expectation of Mary on December 18th. This is a relic, to keep Annunciation out of Lent they celebrated it a week before Christmas. When they restored Annunciation, popular piety was so attached to Dec 18th that it was retained. It was often called the feast of "Our Lady of the O" because of a long "O" chanted after Vespers to express longing for the redeemer. In the Roman Rite breviary there is also an "O" antiphon for this. In various Breviaries there are O antiphons for Raphael (December 24th) and others, and in one Breviary there are 12, starting rather than 7 days before, 12 days before

I will try to post them if I can find them again

At the Benedictine abbey of Fleury the O Antiphons were recited by the abbot and other abbey leaders in descending rank. A gift was given to each member of the community.