Charles Ellicott Commentary Psalms 55:13

"But it was thou, a man mine equal, My companion, and my familiar friend." — Psalms 55:13 (ASV)

But it was ... —Better, But you are a man of my own standing. The word erek is used (Exodus 40:23) of the row of loaves constituting the showbread, and the cognate verb means “to arrange.” Here it may denote rank, but more probably the expression is man of my assessment, and so of the same importance in society. (2 Kings 12:4.) The Septuagint and Vulgate have “of one soul with me.” Symmachus, “of like disposition.” This sense may be implied, though not expressed in the Hebrew.

Guide. —So the old versions: the Hebrew word does denote the head of a tribe or family (Genesis 36:15 and other passages, “duke”), but that meaning seems excluded here by the previous description. Translate as, companion.