The proposed HU root
According to this theory, HU functions as a "sound archetype" running through the sacred vocabulary of many Near Eastern and Indo-European traditions — one of three such archetypes, alongside YA and RA, that proponents claim recur across unrelated languages. Combined with a root for "mind" (drawn from the Sanskrit mana), the theory reads "human" as "luminous mind."
Proponents point to this sound appearing in the Egyptian name Tehuti (Thoth), in the Hebrew and Arabic divine names Allah (rendered AL-LA-HU) and Yahweh (rendered YA-HU-VA-HU), and in the Zoroastrian Ahura Mazda. The Sufi teacher Hazrat Inayat Khan is cited within this theory describing "Hu" as a sacred, unownable name for the divine, repeated by mystics across traditions and languages.
A word of caution
This account should be read as one specific esoteric theory about the word's origin, not as a conclusion accepted by mainstream historical linguistics, which does not derive "human" from this proposed sound archetype.