ADONAI ə dō’ nī, əd ō nā’ ī (אֲדֹנָי, H151). A divine name, tr. “the Lord,” and signifying “sovereignty,” “master.” Its etymology is obscure, but its meaning is certain—God is the ruling Lord. It appears first in Genesis 15:2, 8, and is used often afterward. Its vowels are found in the MT with the tetragrammaton יהוה, H3378, forming the word “Jehovah.” Whenever Heb. readers found these letters, they always substituted for them the word “adonai,” as the name of God was regarded as too sacred to be pronounced.

Bibliography

L. Koehler, Old Testament Theology (1957), 30; J. B. Payne, The Theology of the Older Testament (1962), 146, 147.

International Standard Bible Encyclopedia (1915)

a-do’-ni, ad-o-na’-i (’adhonay): A Divine name, translated "Lord," and signifying, from its derivation, "sovereignty." Its vowels are found in the Massoretic Text with the unpronounceable tetragrammaton YHWH; and when the Hebrew reader came to these letters, he always substituted in pronunciation the word " ’adhonay." Its vowels combined with the tetragrammaton form the word "Yahweh (Yahweh)."

See Names of God.