The "O" Antiphons

O Sapientia! (Wisdom)
O Adonái et Dux domus Israel! (Lord and Leader of the house of Israel)
O Radix Iesse! (Root of Jesse)
O Clavis David! (Key of David)
O Oriens! (Rising Sun)
O Rex gentium! (King of the Nations)
O Emmanuel!

(When the first letters of each invocation are put together and read backwards, the sentence reads 'Ero cras' -- 'I will be [here] tomorrow'.