How do we know the usage of the term Adonai in Genesis 15:2?
As Abram addresses God, he calls him “Lord God.” But in the original language, it’s actually, “Lord Lord (Adonai Yahweh).” So why is it translated, “Lord God”? Because the compound of the two words for Lord signifies that it should be translated that way in English.
We get some pretty interesting translative approaches from the word for Adonai. For instance, the four letters for Yahweh, YHWH, we don’t actually know how to say it anymore. Our best guess is Yahweh. But some people say Jehovah.
The way this came about is that the Hebrews would not pronounce the name of God, instead, they would say Adonai anytime they saw it in the text. This was to make sure they didn’t break the commandment to not take the name of the Lord in vain.
When the Masoretes added vowels in the eighth century BC they used the vowels from Adonai and place them on the YHWH. The Germans don’t have an opening Y sound for any of their words, so they used a J, hence Jehovah.
I would imagine without knowing for sure that the Hebrews would read this as, “Adonai, Adonai.” The name, Yahweh, is God’s formal name for the covenant with Israel. It has its origin in the verb, “to be.”
But the usage for Adonai here is to compound the formal name of God with the other word for Lord and produce, “Lord God.” There are other forms of the compound names of God which change it in English especially to add words like, “ Sovereign Lord,” “Most High God,” and other compound forms for other names for God. Abram was showing honor to God as he spoke with him, humility on his part.