Many people who are familiar with the Old Testament names of God might be quick to answer that Adonai is one of the most common names of God in the Old Testament. This is only partially correct.
The word Adonai is simply the word for “Lord.” Lord is defined in English as “someone or something having power, authority, or influence; a master or ruler.” In 1 Samuel 24:8, 26:17, and 29:8, David refers to Saul as “my lord the king,” and he uses the term Adonai. Likewise, Abner refers to David in the same way in 2 Samuel 3:21, and this is found throughout the book of 2 Samuel as a reference to David. The term is used of other kings as well. Some of Elisha’s followers use the term Adonai to refer to Elisha in 2 Kings 2:19. As can be seen by its usage throughout the Old Testament, Adonai is simply a term of respect that is in keeping with the English definition and usage of the word lord.
It would be more accurate to say that Adonai is used as a description of God or as a title of respect, rather than a name in the proper sense. David would have had no problem addressing God as “Adonai” and then addressing Saul as “Adonai” as well—no one would have been confused by that, just as no one today thinks that referring to the English poet as “Lord Byron” ascribes deity to him.
In the English Old Testament, Adonai is usually translated “Lord”; however, most occurrences of the word Lord in the English Old Testament are not translations of Adonai. God’s special covenant name, YHWH was so holy that, in later years, many Jews feared even to say it. Even today, when they are reading the Hebrew text (which originally had only consonants) they will pronounce YHWH as “Adonai.” In keeping with this tradition, most English versions translate YHWH as “LORD” (in all caps). In general, if the English word is LORD (all capital letters), then the Hebrew word translated is YHWH; and, if the English is Lord (using lowercase letters), whether referring to God or someone else, it is translating Adonai.
Adonai is certainly an apt title for God. While there are other lords who hold sway over limited realms, God is the Lord of all the earth (Joshua 3:11).