Iah is a god of the moon in ancient Egyptian religion, and his name, jˁḥ (sometimes transliterated as Yah, Jah or Aah), simply means "moon." Nevertheless, by the New Kingdom he was less prominent as a moon deity than the other gods with lunar connections, Thoth and Khonsu. As a result of the functional connection between them he could be identified with either of those deities.
He was sometimes considered an adult form of Khonsu, and was increasingly absorbed by him. Iah continued to appear in amulets and occasional other representations, similar to Khonsu in appearance, with the same lunar symbols on his head and occasionally the same tight garments. He differed in usually wearing a full wig instead of a child's sidelock, and sometimes an Atef crown topped by another symbol. As time went on, Iah also became Iah-Djuhty, meaning "god of the new moon."
Iah was also assimilated with Osiris, god of the dead, perhaps because, in its monthly cycle, the moon appears to renew itself. Iah also seems to have assumed the lunar aspect of Thoth, god of knowledge, writing and calculation; the segments of the moon were used as fractional symbols in writing.
One queen was called Iah.