Before the page even refreshed for my original reply, I thought, "huh, I bet the Z is for Zork," and wouldn't you know, it is. That's a pretty good name, when you can grok it from context.

Trying to follow the timeline from that article, it's unclear from context name which came first, Zork, ZIL (Zork Implementation Language), or the word z-machine. I've heard of referring to other systems as [language name/interpreter name/etc]-machine, so that's the context that it reminds me of, but at the time Zork was written, perhaps that convention wasn't established yet? It's before my time, which makes the missing context harder to interrogate solo.