I was probably wrong on suggesting adonai is from the Greek (septuagint) translation. The stuff below puts it in the Hebrew whether it came into the langauge from greek is another matter. Snooker could confirm that.
The Names of God in the Old Testament:
In the Bible God is called by many names which describe different facets of His nature, attributes, and character. A few of the Old Testament names for God and their meanings are: El-Elyon, "The Most High God", Jehovah-Jirah, "The Lord will provide", Jehovah-Shalom, "The Lord of Peace", and El-Shaddai, "The Almighty God". There are three primary names for God - Elohim, Jehovah (Yahweh), and Adonai.
A code system in the King James Version Bible designates which divine name(s) is used in a given passage.
This article begins by looking at how the code system works. It then examines some specific Old Testament passages to see how knowing which Hebrew name for God is used in a passage contributes to a more accurate understanding of the biblical teaching.
The KJV Bible's System for Designating the Divine Names
If you look at the KJV text carefully, you will notice that Deity is variously referred to as "God", "GOD", "Lord", "LORD," or some combination of these terms. These different English words and spelling variations were used by the King James translators to designate the various Hebrew words and names for God in the Old Testament. As has been noted, the three primary Hebrew words for God are Elohim, Jehovah (or Yahweh), and Adonai.............
Adonai. When this word is used in the Hebrew text of Scripture, it is written as "Lord" in the King James Bible. Notice that it is spelled with a capital "L" and lower case "ord." It means "Sovereign," or "Master," and emphasizes the Lordship of God. This word is used more than 300 times in the Old Testament as a designation for God.7
Like Elohim, Adonai is a plural form. In this special plural form it always refers to God.8 The singular form, Adon, is used to designate men who are lords over other people.
Joshua 7:6-7 illustrates how the different names for God in the Hebrew text are coded into the King James Bible:
And Joshua rent his clothes, and fell to the earth upon his face before the ark of the LORD [Jehovah] until the eventide, he and the elders of Israel, and put dust upon their heads. And Joshua said, Alas, O Lord [Adonai] GOD [Jehovah], wherefore hast thou at all brought this people over Jordan, to deliver us into the hand of the Amorites, to destroy us? would to God [Elohim] we had been content, and dwelt on the other side of Jordan!
