Aum (Om)

“This means sun, light and oneness. It comes from the Egyptian, Ahom, which was their first letter (A). The ideogram of Ahom was the golden eagle, still seen with the letter “A” and on innumerable symbols.
In Celtic lands the Alphabet was called Ogham, but this word is pronounced Om or Aum. The connections between the worlds magical alphabets have been noticed and written upon for centuries.”

Source: Astro-Theology Etymology and Sidereal Mythology Tarot Astronomy