nixie

noun

1. A female nix, a water-spirit.

   “The beautiful Nix or Nixie who allures the young fisher or hunter to seek her embraces in the wave which brings his death, the Neck who seizes upon and drowns the maidens who sport upon his banks, the river-spirit who still yearly in some parts of Germany demands tribute of human life, are all forms of the ancient Nicor[.]”

   “The place seems to have been fashioned as a dwelling for dryads and hamadryads, for nixies and pixies, and all the fabled spirits of forest and stream.”

   “Bare from her garters up her flesh appears under the sapphire a nixie’s green.”

   “In medieval times, the image of the double fish tailed siren was called a nixie or evil water spirit. Yet, the nixies were more likely daughters of the primordial goddess named Nyx or mother night, who hovered over ancient waters, rather than evil spirits.”

2. A piece of mail returned as undeliverable.

   “Mailers who are registered participants in the Postal Service's Address Change Service (ACS) system expect to receive their address corrections and nixie notifications by electronic messages;[…].”

   “If you get a response of less than one percent or excessive “nixies” (wrong addresses), rework your copy or get a new list.”

   “Another good reason to use first-class mail is the fact that it will often be forwarded or, if need be, returned to the sender if the address is bad. (In the industry, this is called a “nixie.”) It is important to keep an eye on the nixie rate if you are using first-class mail.”