Mackey's Encyclopaedia of Freemasonry and its Kindred Sciences
Hebrew, A-har-ohne, a word of doubtful etymology, but generally supposed to signify a mountaineer. Mackenzie says the name means the illuminated. He was the brother of Moses, and the first High Priest under the Mosaic dispensation, whence the priesthood established by that lawgiver is known as the Masonic. He is mentioned in the English lectures of the Second Degree, in reference to a certain sign which is said to have taken its origin from the fact that Aaron and Hur were present on the hill from which Moses surveyed the battle which Joshua was waging with the Amalekites, when these two supported the weary arms of Moses in an upright posture, because upon his uplifted hands the fate of the battle depended (see Exodus xvii, 10-12). Aaron is also referred to in the latter section of the Royal Arch Degree in connection with the memorials that were deposited in the Ark of the Covenant. In the Degree or Grade of Chief of the Tabernacle, which is the Twenty-third of the Ancient and Accepted Scottish Rite, the presiding officer represents Aaron, and is styled Most Excellent High Priest. In the Twenty-fourth Degree of the same Rite, or Prince of the Tabernacle, the second officer or Senior Warden also personates Aaron.