[musicale]

"We even knew that it had a joke name, Unix, coined by Brian Kernighan, that was a reference to Multics."

https://multicians.org/unix.html

"Brian Kernighan takes credit for the idea, but adds that 'no one can remember' the origin of the final spelling Unix."

https://en.wikipedia.org/wiki/Unix

Also note that Prof. Kernighan has written a historical memoir about Unix:

https://www.cs.princeton.edu/~bwk/