O Root of Jesse — December 19

O radix Jesse, qui stas in signorum populorum, super quem continebunt reges os suum, quem gentes deprecabuntur: veni ad liberandum nos, jam noli tardare.

http://www.youtube.com/watch?v=VPlfJuq2QZw&feature=channel

O Flower of Jesse's stem, you have been raised up as a sign for all peoples; kings stand silent in your presence; the nations bow down in worship before you. Come, let nothing keep you from coming to our aid. — translation in current Catholic Liturgy of the Hours

O come, thou rod of Jesse, free / Thine own from Satan's tyranny / From depths of hell thy people save / And give them vict'ry o'er the grave. — Verse translation in "O Come, O Come, Emmanuel" (Only the first line has anything to do with the original antiphon.)

O radix Jesse, qui stas in signum populorum — O root of Jesse, who stand as a sign of [= to] the peoples — Isaiah 11:1, 10, 13:22; Revelation 22:16

super quem continebunt reges os suum — over whom kings shall hold [shut] their mouths — Isaiah 52:15

quem gentes deprecabuntur — whom the Gentiles shall implore — 

Isaiah 11:10

jam noli tardare — now do not delay — Habakkuk 2:3; Hebrews 10:37