Heaven, Peace, Serenity: parents seem especially attracted to word names that signal paradise, but Halcyon sounds quite feminine, and might conjure up the sleeping pill Halcion.

Alcyone was the wife of Ceyx, but the happy pair angered the gods by calling each other Zeus and Hera. Ceyx's ship was sunk, Alcyone hurled herself into the sea, but then in sympathy for their grief the gods made the lovers halcyon birds or kingfishers.

This highly unusual name -- the Halycyone was a mythic bird who could calm the seas -- conjures up images of utter peace and tranquility because of the phrase "Halycon days"...and the sleeping pill.