Sin or Suen (Akkadian: 𒀭𒂗𒍪, dEN.ZU) also known as Nanna (Sumerian: 𒀭𒋀𒆠 DŠEŠ.KI, DNANNA) was 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 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 served as a representation of him. He was also associated with boats.

Akkadian is an extinct East Semitic language that was spoken in ancient Mesopotamia from the third millennium BC until its gradual replacement in common use by Old Aramaic among Assyrians and Babylonians from the 8th century BC.