Within the wider Abrahamic Tradition you will see Inexpressibility at the heart of the parallel Mystic schools.
The Qabballah of the Jews; the Taṣawwuf [Sufism] of the Muslims; the Gnostic Texts of Christianity. Key mystic terms like the Jewish Aleph and the Islamic Fana originate here.
The final stage of practice in high Sufism is termed Fana al-Fana, the ‘Annihilation of Annihilation itself’. A Self-Negating Expression, naturally, necessarily.
The Neo-Platonic ‘One’ of Plotinus [sourced in Plato’s Parmenides] was the dominant European Mystical Tradition for a millennia. It was a principal influence on everyone from Thomas Aquinas to Meister Eckhart [‘God is ‘Namelessness’, wrote Eckhart who taught Aristotle at the Sorbonne, and promptly got arraigned by the Vatican].
Reality, wrote Plotinus was: ‘A Nameless Unity, indescribable, undefinable.. never known measure, stands outside number..is under no limit of any kind..is Everything and Nothing..’.
Perhaps no other Mystic influenced all three of the Abrahamic faiths as comprehensively as Plotinus [203-270]. He famously joined Gordian’s march on Persia in order to find his way to India. The campaign failed and he returned to Antioch. In 3rd Century Bharat, the understanding of Shūnyam was still not entirely dead; it would have been a worthwhile visit.