Definition of "nixie"
nixie1
/ˈnɪksi/
noun
plural nixies
Quotations
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.
2011, Katalin Koda, Fire of the Goddess, page 83
nixie2
/ˈnɪksi/
noun
plural nixies
A piece of mail returned as undeliverable.
Quotations
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.
2008, Susan K. Jones, Business-to-Business Internet Marketing, 5th edition, page 15