Nychthemeron. The word of the day was Nychthemeron.

Nychthemeron: noun. A complete cycle of day and night. A word that seems so well defined, but whose solidity is an illusion. On what planet is this day and night taking place? How long is that day and night? Some planets are so snared by the gravity of their star that one face is always in the sun while the other is always in shadow. There is no cycle of day and night there, no rising and setting of the solar disk to herald the next great round. There you can touch eternity.