The Latin noun halcyon, more properly alcyon, was derived from Greek ἀλκυών (= alkuon), incorrectly spelt ἁλκυών (= halkuon), meaning kingfisher. The ancients fabled that the halcyon bred about the time of the winter solstice in a nest floating on the sea, and that it charmed the wind and waves so that the sea was specially calm during the period. The Greek spelling ἁλ- (= hal-) is supposed to have arisen out of the fancy, connected with this fable, that the word was from ἅλς (= hals), sea, and κύων (= kuon), conceiving. Similarly, in Latin, alcyon is a later form of alcedo, probably cognate with English auk.

In Naturalis Historia (Natural History – 77), a vast encyclopaedia of the natural and human worlds, the Roman statesman and scholar Pliny the Elder (23-79) wrote:

translation by John Bostock and Henry T. Riley (1855):
It is for this that the halcyon¹ is more especially remarkable; the seas, and all those who sail upon their surface, well know the days of its incubation. This bird is a little larger than a sparrow, and the greater part of its body is of an azure blue colour, with only an intermixture of white and purple in some of the larger feathers, while the neck² is long and slender. There is one kind that is remarkable for its larger size and its note; the smaller ones are heard singing in the reed-beds. It is a thing of very rare occurrence to see a halcyon, and then it is only about the time of the setting of the Vergiliæ, and the summer and winter solstices; when one is sometimes to be seen to hover about a ship, and then immediately disappear. They hatch their young at the time of the winter solstice, from which circumstance those days are known as the “halcyon days:” during this period the sea is calm and navigable, the Sicilian sea in particular. They make their nest during the seven days before the winter solstice, and sit the same number of days after. Their nests³ are truly wonderful; they are of the shape of a ball slightly elongated, have a very narrow mouth, and bear a strong resemblance to a large sponge. It is impossible to cut them asunder with iron, and they are only to be broken with a strong blow, upon which they separate, just like foam of the sea when dried up. It has never yet been discovered of what material they are made; some persons think that they are formed of sharp fish-Bones, as it is on fish that these birds live. They enter rivers also; their eggs are five in number.
¹ The king-fisher, or Alcedo ispida of Linnæus. There is no truth whatever in this favourite story of the ancients.
² In copying from Aristotle, he has put “collum,” by mistake, for “rostrum,” the “beak.”
³ This bird in reality builds no nest, but lays its eggs in holes on the water side. The objects taken for its nest are a zoophyte called halcyonium by Linnæus, as Cuvier informs us, and similar in shape to a nest.

In English, since the late 14^th century, halcyon has been used as a poetic name for the kingfisher.

The noun was used figuratively to denote calm, quietude. The following is from A Commentary upon the Gospel according to St. Matthew (1656), by John Trapp (1601-69), Church of England clergyman and writer on theology:

When the Pope had excommunicated him [= Luther], and the Emperour proscribed him, the Lord put into the heart of the Duke of Saxony to hide him for ten moneths: In which space the Pope dyed, the Emperour had his hands full of the French wars, and the Church thereby obtained an happy Halcyon.

The expression halcyon days is from Greek ἀλκυονίδες ἡμέραι (= alkuonides hemerai), in Latin alcyonei dies, also alcyonides, alcedonia, which designated fourteen days of calm weather, anciently believed to occur about the winter solstice when the halcyon was brooding.

In the sense of a period of peace and happiness, halcyon days was used for example by the English poet and playwright William Shakespeare (1564-1616) in The First Part of King Henry the Sixth (1591?); Reignier, a French lord, asks Charles, Dauphin of France, if Orléans should be abandoned to the English:

(Folio 1, 1623)
– Reignier: My Lord, where are you? what deuise you on?
Shall we giue o’re [= over] Orleance, or no?
– Joan: Why no, I say: distrustfull Recreants,
Fight till the last gaspe: Ile be your guard.
– Charles: What shee sayes, Ile confirme: wee’le fight
it out.
– Joan: Assign’d am I to be the English Scourge.
This night the Siege assuredly Ile rayse:
Expect Saint Martins Summer, Halcyons dayes,
Since I haue entred into these Warres.

Various superstitions have been associated with the kingfisher, some of which it shares with the halcyon, especially the belief that a dried specimen hung up indicated by its position the direction in which the wind was blowing. In the following from The Tragedy of King Lear (around 1605), Shakespeare makes the Earl of Kent mention this superstition:

(Folio 1, 1623)
That such a slaue as this should weare a Sword,
Who weares no honesty: such smiling rogues as these,
Like Rats oft bite the holy cords a twaine,
Which are t’intrince, t’vnloose: smooth euery passion
That in the natures of their Lords rebell,
Being oile to fire, snow to the colder moodes,
Reuenge, affirme, and turne their Halcion beakes
With euery gall, and varry of their Masters,
Knowing naught (like dogges) but following.

In A Natural History of Birds, intended chiefly for young persons, the English author Charlotte Smith (1749-1806) wrote:

(1807 edition)
I have once or twice seen a stuffed bird of this species hung up to the beam of a cottage ceiling. I imagined that the beauty of the feathers had recommended it to this sad preeminence, till on inquiry I was assured, that it served the purpose of a weather vane; and though sheltered from the immediate influence of the wind, never failed to show every change by turning its beak from the quarter whence the wind blew. So that some superstition as to the connexion between the wind and the Halcyon seems, like many other relicts of almost forgotten prejudices, to linger still in our cottages.