Mesopotamian lunar god
Sin () or Suen (, ) also known as Nanna ( ) is the Mesopotamian god representing the moon. While these two names originate in two different languages, respectively Akkadian and Sumerian, they were already used interchangeably to refer to one deity in the Early Dynastic period. They were sometimes combined into the double name Nanna-Suen. A third well attested name is Dilimbabbar (𒀭𒀸𒁽𒌓). Additionally, the name of the moon god could be represented by logograms reflecting his lunar character, such as d30 (𒀭𒌍), referring to days in the lunar month or dU4.SAKAR (𒀭𒌓𒊬), derived from a term referring to the crescent. In addition to his astral role, Sin was also closely associated with cattle herding. Furthermore, there is some evidence that he could serve as a judge of the dead in the underworld. A distinct tradition in which he was regarded either as a god of equal status as the usual heads of the Mesopotamian pantheon, Enlil and Anu, or as a king of the gods in his own right, is also attested, though it only had limited recognition. In Mesopotamian art, his symbol was the crescent. When depicted anthropomorphically, he typically either wore headwear decorated with it or held a staff topped with it, though on "kudurru" the crescent alone serves as a representation of him. He was also associated with boats.
The goddess Ningal was regarded as Sin's wife. Their best attested children are Inanna (Ishtar) and Utu (Shamash), though other deities, for example Ningublaga or Numushda, could be regarded as members of their family too. Sin was also believed to have an attendant deity (sukkal), Alammuš, and various courtiers, such as Nineigara, Ninurima and Nimintabba. He was also associated with other lunar gods, such as Hurrian Kušuḫ or Ugaritic Yarikh.
The main cult center of Sin was Ur. He was already associated with this city in the Early Dynastic period, and was recognized as its tutelary deity and divine ruler. His temple located there was known under the ceremonial name Ekišnugal, and through its history it was rebuilt by multiple Mesopotamian rulers. Ur was also the residence of the "en" priestesses of Nanna, the most famous of whom was Enheduanna. Furthermore, from the Old Babylonian period onward he was also closely associated with Harran. The importance of this city as his cult center grew in the first millennium BCE, as reflected in Neo-Hittite, Neo-Assyrian and Neo-Babylonian sources. Sin's temple survived in later periods as well, under Achaemenid, Seleucid and Roman rule. Sin was also worshiped in many other cities in Mesopotamia. Temples dedicated to him existed for example in Tutub, which early on was considered another of his major cult centers, as well as in Urum, Babylon, Uruk, Nippur and Assur. The extent to which beliefs pertaining to him influenced the Sabians, a religious community who lived in Harran after the Muslim conquest of the Levant, is disputed.
Names.
While it is agreed that the two primary names of the Mesopotamian moon god, Nanna and Sin (Suen), originated in two different languages, respectively Sumerian and Akkadian, it is not possible to differentiate between them as designations of separate deities, as they effectively fully merged at an early date. Gebhard J. Selz points out this phenomenon is already attested in sources from Lagash from the Early Dynastic period, where the name Nanna does not appear, and Sin is the form used in both Sumerian and Akkadian context. The process of conflation presumably started prior to the invention of cuneiform. Sometimes the double name Nanna-Suen was used, as evidenced for example by a short theological text from the Ur III period listing the main deities of the official pantheon. It is sometimes used to refer to this god in modern Assyriological publications too.
Nanna.
The precise etymology of the name Nanna is unknown, though it is agreed that it is not a genitive construction. It is first attested in the Uruk period. In earliest cuneiform texts from Uruk and Ur it was written as (d)LAK-32.NA, with NA possibly serving as a phonetic complement. The name of the city of Ur (Urim) was accordingly written as LAK-32.UNUGki (𒋀𒀕𒆠), "residence of Nanna", per analogy with toponyms such as Zabalam, INANNA.UNUGki. In later periods LAK-32 coalesced with ŠEŠ (the ideogram for "brother"), and Nanna's name came to be written as dŠEŠ+KI or dŠEŠ.KI, though phonetic spellings such as "na-an-na" are attested too, for example as glosses in lexical lists.
In early Assyriological scholarship it was often assumed that the variant form Nannar was the standard form of the name, but further research demonstrated that it does not predate the Old Babylonian period. The writing "dna-an-na-ar" is attested in Akkadian and Elamite texts, and was the result of linguistic contamination between the theonym Nanna and the common Akkadian noun "nannaru", "light". As an epithet, "nannaru" could be used to address the moon god, but also Ishtar and Girra.
It is uncertain if the theonym Nanum attested in a theophoric name from Umma is a derivative of Nanna, while Nanni worshiped in Mari and in the kingdom of Khana was a female deity and might be related to Nanaya rather than the moon god.
Sin.
In Akkadian the moon god was called Sin (Sîn) or Suen (Su’en). The former is the standard reading of the name from the Old Babylonian period onward, while the latter was presumably the older uncontracted pronunciation. The etymology of this name remains uncertain. One of the inscriptions of Gudea from the third millennium BCE refers to Sin as a god "whose name nobody can explain", which might be an indication that his name was already unclear and a subject of scribal speculation during his reign.
The name Sin was typically written in cuneiform as dEN.ZU, as possibly already attested in a text from the Uruk period, though oldest certain examples, such as entries in the god lists from Fara and Abu Salabikh, only date back to the Early Dynastic period. Most likely it initially developed as a rebus meant to graphically resemble the names of gods whose names had Sumerian etymologies and contained the element EN, for example Enlil. Various phonetic spellings are also attested, for example "sú-en", "sí-in", "si-in" and "se-en". The large variety of these variants might indicate that the first sibilant was difficult to render in cuneiform. In early Akkadian, the sound /s/ was an affricate [ts], which would explain its initial representation with Z-signs and later with S-signs. 
A variant form of Sin's name, Suinu, is also attested in texts from Ebla. It has been pointed out that an Eblaite lexical list with the entry "sú-i-nu" is the oldest available attestation of a phonetic spelling of the name. However, the logogram dEN.ZU was also used in this city. Additionally, in a translation of an Akkadian text written in the Ugaritic alphabetic script the name is rendered as "sn" (KTU 1.70, line 4), while in Aramaic the variants "sn", "syn" and "šn" are attested. In the Masoretic Text of the Hebrew Bible Sin's name is rendered as "san" in the theophoric names Sennacherib (Sîn-aḫḫe-erība) and Sanballat (Sîn-uballiṭ). Alfonso Archi argues that the theonym "syn" attested in a number of inscriptions from South Arabia should be interpreted as a variant of Sin's name too, and suggests vocalizing it similarly to the Eblaite form of the name. However, Manfred Krebernik concludes that no certain cognates of Sin's name have been identified in other Semitic languages, and "syn" (or "sn"), who according to him is only known from Thamudic inscription from Hadhramaut, should instead be interpreted as Sayin, the local sun god.
From the Old Babylonian period onward Sin's name could be represented by the logogram d30 (𒀭𒌍), derived from the cuneiform numeral 30, symbolically associated with him due to the number of days in the lunar month. It was originally assumed that an even earlier example occurs in the writing of a personal name from the Ur III period, but subsequent research demonstrated that this was the result of erroneous collation. In the first millennium BCE d30 became the most common writing. For example, in the text corpus from Neo-Babylonian Uruk only a single text, a "kudurru" inscription of Ibni-Ishtar, uses dEN.ZU instead of d30. Uncommonly dNANNA was used in Akkadian texts as a sumerogram meant to be read as Sin.
Dilimbabbar.
Next to Sin and Nanna, the best attested name of the moon god is dAŠ"-im4-babbar" (𒀭𒀸𒁽𒌓). It was originally assumed that it should be read as Ašimbabbar, though it was subsequently proved that this depended on an erroneous collation. By 2016 the consensus view that Dilimbabbar is the correct reading was established based on the discovery of multiple passages providing phonetic syllabic spellings. The name can be translated as "the shining one who walks alone". This meaning was originally established based on the now abandoned reading of the name, but it is still considered a valid translation. An alternate proposal relying on homophony of the element "dilim" and the logogram "dilim2" (LIŠ) is to explain Dilimbabbar as "the shining bowl". The term "dilim2" was a loan from Akkadian "tilimtu", "bowl". Piotr Steinkeller notes that it is not impossible both proposals regarding the meaning of Dilimbabbar are correct, and that the scribes might have intentionally created puns depending on the well attested tradition of referring to the moon as a unique or solitary celestial body.
Dilimbabbar is already attested in the Early Dynastic god list from Abu Salabikh. The "Zame Hymns" from the same period link this title with the worship of the moon god in Urum (Tell Uqair). It is not certain if at this point in time it was understood as a title of Sin or as the name of a distinct deity of analogous character. Mark Glenn Hall notes that the absence of theophoric names invoking the moon god under this name from available sources might indicate that if Dilimbabbar was ever understood as a distinct deity this tradition disappeared very early on. However, Manfred Krebernik and Jan Lisman point out that in the "Temple Hymns" (hymn 37) Dilimbabbar is addressed as a shepherd of Sin, which they argue might be a relic of an intermediate stage between the existence of two independent moon gods and their full conflation.
For unknown reasons the name Dilimbabbar is absent from all the other known Early Dynastic sources, as well as these from the subsequent Sargonic and Ur III periods, with the next oldest attestation being identified in an inscription of Nur-Adad of Larsa from Ur from the Isin-Larsa period, which might reflect a rediscovery of the name by scribes under hitherto unknown circumstances. It remained in use through subsequent periods, down to the first millennium BCE.
The Akkadian epithet Namraṣit was considered analogous to Dilimbabbar, as attested in the god list "An = Anum" (tablet III, line 26). It can be translated as "whose rise is luminous". Steinkeller points out that it is not a direct translation of Dilimbabbar, as it effectively leaves out the element "dilim". Bendt Alster assumed that the equivalence was the result of late reinterpretation.
Character.
Sin was understood both as an anthropomorphic deity representing the moon, and as the astral body itself. He was responsible for providing light during the night. His luminous character could be highlighted with epithets such as "the luminary of the heavens and earth" ("nannār šamê u erṣeti") or "the luminary of all creation" ("nannār kullati binīti"). The growth of the moon over the course of the month was reflected in comparing Sin to the growth of fruit (Akkadian "inbu", Sumerian "gurun") as attested in Neo-Assyrian and Neo-Babylonian sources, especially hemerologies. However, it was not applied consistently as a designation for a specific phase of the moon. Lunar eclipses were believed to be the result of Sin being surrounded by seven evil "utukku" sent by Anu.
Next to his astral aspect, Sin's other main role has been described as that of a pastoral deity. He was associated with cattle and with dairy products. This link is reflected in his secondary names Abkar, "shining cow", and Ablulu, "the one who makes the cows abundant". He could be addressed as a herdsman in astral context, with stars being poetically described as his herd. In addition to cows, he could also be associated with sheep and with wild animals inhabiting steppes, especially ibexes and gazelles.
Sin was perceived as a benign deity who could be petitioned