Adon is a real Hebrew word, and it does mean what English "Lord" means: a master, an owner, a superior authority. Sarah calls Abraham her adon. David is called adon. YHWH is sometimes called adonai, "my lord," as a title of reverent address. The word has legitimate semantic weight and an honored place in the Tanakh.

Adon is not, however, the same word as YHWH. The Tetragrammaton is a Name; adon is a title. When the Second Temple qere convention substituted Adonai aloud for the written YHWH, it preserved the Name in writing but spoke the title. The Septuagint then reached for kurios to render the spoken substitute into Greek. The Vulgate rendered it Dominus. English translators carried LORD in small caps to signal YHWH and Lord in ordinary type to signal adon. The distinction survives on the page if you know what the small caps mean. The distinction rarely survives in the reader's ear. Adon is the word the English Bible has handed you for almost everything. YHWH is the word the Hebrew insisted on for the One who made the covenant.