... Delta (uppercase Δ, lowercase δ) ... is the fourth letter of the Greek alphabet. In the system of Greek numerals it has a value of 4. It was derived from the Phoenician letter Dalet.

Letters that come from delta include Latin D and Cyrillic Д. A river delta (originally, the Nile River delta) is so named because its shape approximates the upper-case letter delta (the shape is a triangle) ...

Dalet (dāleth, also spelled Daleth or Daled) is the fourth letter of many Semitic alphabets ... The letter is based on a glyph of the Middle Bronze Age alphabets, probably called dalt 'door' (door in Modern Hebrew is delet), ultimately based on a hieroglyph depicting a door.

... Sorrowing, then, the two women placed Osiris's coffer on a boat, and when the goddess Isis was alone with it at sea, she opened the chest and, laying her face on the face of her brother, kissed him and wept. The myth goes on to tell of the blessed boat's arrival in the marshes of the Delta, and of how Set, one night hunting the boar by the light of the full moon, discovered the sarcophagus and tore the body into fourteen pieces, which he scattered abroad; so that, once again, the goddess had a difficult task before her. She was assisted, this time, however, by her little son Horus, who had the head of a hawk, by the son of her sister Nephtys, little Anubis, who had the head of a jackal, and by Nephtys herself, the sister-bride of their wicked brother Set. Anubis, the elder of the two boys, had been conceived one very dark night, we are told, when Osiris mistook Nephtys for Isis; so that by some it is argued that the malice of Set must have been inspired not by the public virtue and good name of the noble culture hero, but by this domestic inadventure. The younger, but true son, Horus, on the other hand, had been more fortunately conceived - according to some, when Isis lay upon her dead brother in the boat, or, according to others, as she fluttered about the palace pillar in the form of a bird.

The four bereaved and searching divinities, the two mothers and their two sons, were joined by a fifth, the moon-god Thoth (who appears sometimes in the form of an ibis-headed scribe, at other times in the form of a baboon), and together they found all of Osiris save his genital member, which had been swallowed by a fish. They tightly swathed the broken body in linen bandages, and when they performed over it the rites that thereafter were to be continued in Egypt in the ceremonial burial of kings, Isis fanned the corpse with her wings and Osiris revived, to become the ruler of the dead. He now sits majestically in the underworld, in the Hall of the Two Truths, assisted by forty-two assessors, one from each of the principal districts of Egypt; and there he judges the souls of the dead. These confess before him, and when their hearts have been weighed in a balance against a feather, receive, according to their lives, the reward of virtue and the punishment of sin ...