Halcyon is another name for the kingfisher, which find their name from the Greek myth of Alcyone and Ceyx.
When Ceyx lost his brother, he felt the gods had turned hostile toward him. He decided, therefore, to voyage to consult the oracle of Apollo. Alcyone tried desperately to persuade him to forego the trip. She had grown up in the palace of the King of the Winds and knew well the violence of the winds at sea. With tears and sobs she bade him farewell, then fell senseless to the ground in grief as he boarded the ship and departed.
The first night out, the east wind began to blow a gale and amid the roar of the thunder, the swelling sea lifted to the heavens, scattering its foam among the clouds, then dropped away to the deep sea bottom. According to Bullfinch's Mythology:
"Rain falls in torrents, as if the skies were coming down to unite with the sea. When the lightning ceases for a moment, the night seems to add its own darkness to that of the storm; then comes the flash, rending the darkness asunder, and lighting up all with a glare.... Some of the seamen, stunned by the stroke, sink, and rise no more; others cling to fragments of the wreck. Ceyx, with the hand that used to grasp the scepter, holds fast to a plank, calling for help,- alas, in vain. But oftenest on his lips was the name of Alcyone.”
Morpheus was sent in a dream to tell Alcyone of her loss.
When her husband's body appeared before her floating toward shore, Alcyone, filled with grief, threw herself into the sea. But before she hit water, she changed instantly into a bird. As she flew skimming along the water surface toward the lifeless body, her throat poured forth sounds full of grief, her voice, lamentation. When she touched Ceyx's mute and bloodless body, she enfolded it with her new-formed wings, and tried to kiss it with her horny beak. Feeling her deep grief, the gods out of pity changed the couple into a pair of kingfishers.
Ever since, the legend goes, Alcyone carries her dead mate to his burial, then builds a nest and launches it out to sea. There, she lays her eggs and hatches her chicks, brooding over her sea-borne nest, seven placid days before the Winter Solstice and seven becalmed days after. While she is brooding, the sea is held unusually calm. These are known as the halcyon days.