Abstract The oldest record of the notion of “mercy”, raḥmān, in Aramaic is known from a bilingual text in which the word is the translation of the Akkadian rēmēnû. The latter is used in Mesopotamian onomastics, hymns and prayers, which delivered the oldest formulae of calls for the mercy of gods, especially in a recurrent expression: “the merciful god, that is good to pray,” translated verbatim in the Aramaic text of the statue of Tell Fekheryeh. Almost a thousand years later, the same wording has been inherited unchanged in Palmyrene Aramaic. Nevertheless, the Palmyrene interest on the divine epithet raḥmān and its revival in Palmyrene epigraphy may be explained by the influence of the new Roman concept of clementia. Meanwhile, this contribution proposes to outline a chronology of the Aramaic inscriptions from Syria and Palestine, in which raḥmānāʾ is either the main substitute for the divine name, or a major divine epithet. As the Akkadian phonetic assimilates the consonant <ḥ> to the laryngeal <ʾ> but preserves the velar <ḫ>, the supposed East Semitic root was rḥm, not rḫm. On the contrary, in the Arabian Peninsula, the earliest attested root is rḫm, as evidenced by South Arabic onomastics or toponymy. A late use of rḥm in South Arabic as a verb or noun is the result of a loan from Aramaic and does not appear until the fifth century AD. The first South Arabian inscriptions naming the monotheistic god raḥmānn are preceded by the Palmyrene inscriptions by almost two centuries and are contemporary with the Jewish-Aramaic inscriptions in the Palestinian synagogues, which call the God Raḥmānāʾ. Late, the Aramaic epithet was transferred to the Arabic al-raḥmān, through South Arabian.