(poetic) A kingfisher said in classical mythology to nest on the sea, thereby calming the waters. / The dead body of such a bird, said in Tudor times to act as a weather vane when hung from a beam.

Pertaining to the halcyon or kingfisher. / (figuratively) Calm, undisturbed, peaceful, serene.

plural of halcyon

Period of calm during the winter, when storms do not occur. / (idiomatic) A period of calm, usually in the past and often nostalgic.