On Psa 110:1:
. . . Ps. 110 was actually
written by a psalmist to praise David and his subsequent descendants. The
Hebrew term לַאדֹנִי ("to my lord") in verse one, which the LXX
renders as τω κυρίω μου, is
the common means by which to refer to anyone of higher rank or authority. There
are ample examples inside and outside of the Hebrew Bible of the term אדני ("my
lord") referring to a higher-ranking individual.
However, because the term אדני ("my
lord" or adonai) had already become the standard replacement for
the Tetragrammaton (יהוה) when reading Hebrew texts, and because the LXX does
not distinguish between יהוה and אדני, rendering both as κύριος ("lord”),
the Greek phrase κυρίω μου ("my lord") came to be identified more so
with the "divine" than its original use in the Hebrew of Ps. 110,
where it was clearly a euphemism for referencing the enthroned king of Israel. (Robert
R. Cargill, Melchizedek, King of Sodom: How Scribes Invented the Biblical
Priest-King [Oxford: Oxford University Press, 2019], 83)
On the use of אדני as a referent to “a higher-ranking individual”:
See Gen 23:6, 11, 15 where the
Hittites respectfully refer to Abraham as אדני and as a “prince” (נשיא) during
the negotiations for the Makpelah Cave. The word אדני is used in Gen. 24:18,
when Rebekah refers to Abram’s servant at the well and offers him drink. In
Gen. 32-33, Jacob refers to his elder brother, Esau, as אדני repeatedly. The soldier-author
of Lachish Letter 3 repeatedly uses אדני (“my lord”) to address his commanding
officer. (Ibid., 162 n. 5)