“Josephos has preserved an extract from the Egyptian historian Manetho, which relates the Egyptian version of the story of the Exodus as it was told in the second century before our era. In this it is stated that the earlier name of Moses was Osarsiph, and that he had been priest of Heliopolis or On.
Here it is evident that Moses and Joseph have been confounded together. The name of Joseph, who married the daughter of the priest of On, has been decomposed into two elements, the first of which is the divine name Jeho, and this has been changed into its supposed Egyptian equivalent Osar or Osiris.
It is clear that, whatever might have been his opinion about the name of Joseph, Manetho had no doubt that that of Moses was purely Israelitish. It was not until he had become the Israelitish lawgiver and had ceased to be an Egyptian priest that Osarsiph took the name of Moses.
But Moses finds no satisfactory etymology in the pages of the Hebrew lexicon. It stands alone among Hebrew proper names, like Aaron and David. We do not hear of any other persons who have borne the name. If, therefore, it is Semitic, it must belong to an older stratum of Semitic nomenclature than that preserved to us in the Old Testament. We must look to other branches of the Semitic stock for its explanation.
There is only one other branch of the Semitic family whose records are earlier than those of the Hebrews. Arabic literature begins long after the Christian era, when Jewish and Greek and even Christian names and ideas had penetrated into the heart of the Arabian peninsula.
The Arabic language, moreover, belongs to a different division of the Semitic family of speech from that to which Hebrew belongs. To compare Arabic and Hebrew together is like comparing Latin with modern German. There is, however, one Semitic language which has the closest affinities to Hebrew, and this is also the language of which we possess records older than those of the Hebrew Scriptures. I need hardly say that I am referring to Assyrian.
Now the Assyrian equivalent of the Hebrew Mosheh, “Moses,” would be mâsu, and, as it happens, mâsu is a word which occurs not unfrequently in the inscriptions. It was a word of Accadian origin, but since the days of Sargon of Accad had made itself so thoroughly at home in the language of the Semitic Babylonians as to count henceforth as a genuinely Semitic term.
Mâsu signified as nearly as possible all that we mean by the word “hero.” As such, it was an epithet applied to more than one divinity; there was one god more especially for whom it became a name.
This god was the deity sometimes called Adar by Assyrian scholars, sometimes Nin-ip, but whose ordinary name among the Assyrians is still a matter of uncertainty. He was a form of the Sun-god, originally denoting the scorching sun of mid-day. He thus became invested with the sterner attributes of the great luminary of day, and was known to his worshippers as “the warrior of the gods.”
The title of Mâsu, however, was not confined to Adar. It was given also to another solar deity, Merodach, the tutelar god of Babylon and the antagonist of the dragon of chaos, and was shared by him with Nergal, whose special function it was to guard and defend the world of the dead.
But Nergal himself was but the sun of night, the solar deity, that is to say, after he had accomplished his daily work in the bright world above and had descended to illuminate for a time the world below.”
A.H. Sayce, Lectures on the Origin and Growth of Religion as Illustrated by the Religion of the Ancient Babylonians, 5th ed., London, 1898, pp. 45-7.