1 The title of this Psalm, which we have just chanted and proposed to discuss, is, “On the end, for Idithun, a Psalm for David himself.” Here then we must look for, and must attend to, the words of a certain person who is called Idithun; and if each one of ourselves may be Idithun, in that which he sings he recognises himself, and hears himself speak. For you may see who was called Idithun, according to the ancient descent of man; let us, however, understand what this name is translated, and seek to comprehend the Truth in the translation of the word. According therefore to what we have been able to discover by enquiry in those names which have been translated from the Hebrew tongue into the Latin, by those who study the sacred writings, Idithun being translated is “over-leaping them.” Who then is this person “over-leaping them”? Or who those whom he has “over-leaped”?...For there are some persons, yet clinging to the earth, yet bowed down to the ground, yet setting their hearts on what is below, yet placing their hopes in things that pass away, whom he who is called “over-leaping them” has “over-leaped.”
Source: The Enarrations, or Expositions, on the Psalms (New Advent)