When we read a reference to "The Lord" in the Old Testament, and particularly in the Psalms such as is found in Psalm 18 (1 I love you, O LORD, my strength. The LORD is my rock and my fortress and my deliverer, my God, my rock, in whom I take refuge, my shield, and the horn of my salvation, my stronghold.), should we consider "The Lord" to be a reference to Jesus? If not, then to whom is that addressed?

Do all the OT references to "Lord" use the same Hebrew word? If so, what is that word? If not, what are the various Hebrew words?

What I found:

"Answer: It can be very confusing to understand how the different titles used for God are used in the Bible. Part of the problem is that different Bible translations use the terms somewhat differently. The primary reason for the use of LORD in place of God's Hebrew name is to follow the tradition of the Israelites in not pronouncing or spelling out God's name. So, when God's Hebrew name "YHWH" is used in the Old Testament, English translations usually use "LORD" in all caps or small caps. Also, since ancient Hebrew did not use vowels in its written form, it is not entirely clear how God's name should be spelled or pronounced. It could be Yahweh, or Jehovah, or Yehowah, or something else.

As stated above, when "LORD" in all caps or small caps occurs in the Old Testament, it is a replacement for an occurrence of God's Hebrew name "YHWH," also known as the Tetragrammaton. This is fairly consistent throughout all the different English translations of the Bible. When "Lord" occurs in the Old Testament, referring to God, it is usually a rendering of "Adonai (https://www.gotquestions.org/meaning-of-Adonai.html)," a name/title of God that emphasizes His lordship. LORD/YHWH and Lord/Adonai are by far the two most consistent renderings throughout all the different English Bible translations.

In the Old Testament, when "God" is used, it is usually a rendering of the general Hebrew word for God, "Elohim." When "LORD GOD" or "Lord GOD" occurs, it is usually a rendering of a dual name for God "Adonai YHWH." The Hebrew term "YHWH Sabaoth" is usually rendered "Lord of Hosts." The Hebrew term "YHWH Shaddai" is usually rendered "LORD Almighty." The Old Testament uses many different names and titles to refer to God, to emphasize certain aspects of His person and attributes. This can result in confusion in translation, but in the original Hebrew, it was done entirely in an effort to glorify and magnify God's name."

https://www.gotquestions.org/LORD-GOD-Lord-God.html

Now, answer your original question. :)

I will have to ponder it.

Shema, Yisrael, Adonai Eloheinu, Adonai Echad,
"Hear, O Israel: the LORD our God, the LORD is one", This is a famous Hebrew prayer. Adonai is used here. I recently attended a combination Christmas/Hanukkah service and the Jewish person used that prayer. I had only heard it once before but never looked up the meaning. The Jews /Muslims/ Christians are Monotheistic but the concept of Trinity is confusing to many people.