The seven O Antiphons are known in the Liturgy as the Greater Ferias. These prayers come from the Breviary’s Vespers during the Octave before Christmas Eve, a time which is called the “Golden Nights.”
Each Antiphon begins with “O” and addresses Jesus with a unique title which comes from the prophecies of Isaias and Micheas (Micah), and whose initials, when read backwards, form an acrostic for the Latin “Ero Cras” which means “Tomorrow I come.” Those titles for Christ are:
Sapientia
Adonai
Radix Jesse
Clavis David
Oriens
Rex Gentium
Emmanuel
Ero Cras – Tomorrow I come