"UNIX"

[Chris Rawnsley]

Well I've managed to dig up something.

"Coined in 1969 to describe a specific computer operating system, the
term "Unix" now covers a whole host of variations, including Linux,
FreeBSD, and Solaris. The name was intended as a pun on an earlier
system called "Multics" (Multiplexed Information and Computing
Service). This pun is the key to understanding the acronym, since the
word "uniplexed" does not mean anything in particular. ("Multiplexed"
refers to a communications system able to carry many messages
simultaneously.)"
- http://www.neoworks.com/info/technologies/glossary/

Wahey! Mystery solved.