Omnis terra adoret te, Deus, et psallat tibi: psalmum dicat nomini tuo, Altissime.
“All earth shall worship you, O God, and sing psalms for you, shall sing a psalm to your name, O Most High.” (Ps 65(64):4)
This is a chant in the fourth mode. This tonality often produces endings that do not really sound like endings and leave the listeners in a sort of suspended state.
In this case, it is the word Altissime (“you, the Most High”) that creates such an open ending. Altissime is not part of the Vulgate text of this psalm. Wherever it comes from, the medieval singers might have noticed that difference. Altissimus is often used as a translation of the Hebrew El or Elohim, giving a name to someone who cannot be named (as long as he does not reveal his name – he does so in Exod 3, but that does not make it any easier to understand).
The psalm verse has us “sing a psalm to his name,” and then the antiphon adds a fourth-mode Altissime in place of that name. We feel compelled to say something to describe what cannot be described. For today, let us go with “Most High,” knowing that this raises more questions than it answers.