The problem involved in this double name has not yet been definitely solved.  Evidence seems to favour the view that Ramman ("the thunderer") as the name current in Babylonia, whereas Adad was more common in Assyria.  To judge from analogous instances of a double nomenclature, the two names revert to two different centres for the cult of a storm-god, though it must be confessed that up to the present it has been impossible to determine where these centres were.  A god Hadad who was a prominent deity in ancient Syria is identical with Adad, and in view of this it is plausible to assume—for which there is also other evidence—that the name Adad represents an importation into Assyria from Aramaic districts.  Whether the same is the case with Ramman, identical with Rimmon, known to us from the Old Testament as the chief deity of Damascus, is not certain though probable.  On the other hand the cult of a specific storm-god in ancient Babylonia is vouched for by the occurrence of the sign Im—the "Sumerian" or ideographic writing for Adad-Ramman—as an element in proper names of the old Babylonian period.  However this name may have originally been pronounced, so much is certain,—that through Aramaic influences in Babylonia and Assyria he was identified with the storm-god of the western Semites, and a trace of this influence is to be seen in the designation Amurru, also given to this god in the religious literature of Babylonia, which as an early name for Palestine and Syria describes the god as belonging to the Amorite district.
    In Syria Hadad is hardly to be distinguished from a solar deity.  The process of assimilation did not proceed so far in Babylonia and Assyria, but Shamash and Adad became in combination the gods of oracles and of divination in general.  Whether the will of the gods is determined through the inspection of the liver of the sacrificial animal, through observing the action of oil bubbles in a basin of water or through the observation of the movements of the heavenly bodies, it is Shamash and Adad who, in the ritual connected with divination, are invariably invoked.  Similarly in the annals and votive inscriptions of the kings, when oracles are referred to, Shamash and Adad are always named as the gods addressed, and their ordinary designation in such instances is bēlē biri, "lords of divination."  The consort of Adad-Ramman is Shala, while as Amurru his consort is called Aschratum. (Encyclopedia Britannica, Chambers, v.1, 1910)