HALCYON (ALCEDO), n. The Kingfisher. Halcyon days are days of tranquility and calm; so called because fr a few days in the season of storms, when the kingfisher was rearing its young, the gods used to curb the fury of the elements. So at least, the simple ancient was pleased to believe. It was an abominable superstition, altogether beneath contempt, and not at all comparable to the Christian belief that at midnight on Christmas eve the weather is moderated in deference to the birds and beasts which wake at that hour to worship the Savior.
2007 Update: HALCYON, adj. At ease, peaceful, as the life available to someone who has 10% more than you have managed to scrabble together so far.