Halcyon
Etymology
From Greek halkyōn, a name for the kingfisher, which the ancients linked (by folk etymology) to hals, "sea," and kyōn, "conceiving." Greek myth held that the halcyon nested on the sea around the winter solstice and that the gods calmed the waters for it, giving fourteen days of windless peace — the original "halcyon days." Those calm days of the myth are the source of today’s sense of tranquil, blissful ease.
adjective · /HAL-see-un/
Idyllically calm, peaceful, and prosperous, especially of a remembered past time.
What it names
The golden, untroubled quality of a period looked back on as serene and happy — most often in the phrase "halcyon days."
Example
They spoke of the summer before the war as the halcyon days, when nothing seemed to weigh on anyone.
Related idea
Idyllic stresses picturesque, pastoral perfection; halcyon adds the note of calm and of a past looked back on with longing.