A halcyon time is calm, peaceful, happy and carefree. The fabled halcyon days of calm weather are traditionally the seven days each side of the winter solstice on 21 December.
The story goes back to a Greek legend that the kingfisher nested in the sea at this time of year and that its floating nest brought calm to wind and water. A romantic version of the legend was told by the Roman poet Ovid about Ceyx and Alcyone.
She was the daughter of Aeolus, the god of the winds, and he was the son of the morning star. Ceyx was lost at sea and Alcyone was inconsolable. The gods took pity on them, turning them into kingfishers so that they might continue to live together. When they mated each year at the winter solstice the gods calmed the winds and seas so Alcyone might brood her eggs safely.
Alcyone’s name came from the Greek name for the kingfisher, alkuon. It became halcyon in Latin, because of a mistaken belief that its real source was two Greek words that meant “conceiving on the sea” (folk etymology has a very long history).
When the word first came into English, in reference to the Greek legend, it was usually written in the Greek way, but when it became a general word meaning peaceful or calm, the Latin form took over.