The second of the O Antiphons is O Adonai. Adonai was one of the Hebrew names for God, usually used in place of the unspoken Tetragrammaton. It is most often translated as Lord in our English Bibles. In Jesus God has made Himself fully known to his people and would redeem them from sin and death as He did the people of Israel from Egypt.

O Adonai, and leader of the house of Israel,
who appeared to Moses in the fire of the burning bush
and gave him the law on Sinai:
Come and redeem us with an outstretched arm.