in search of Hebrew etymology

Dani and I were discussing sha'atnez, the torah-forbidden mixture of linen and wool, over lunch. (No, I don't remember how we got there. These things happen.) I said that word has too many letters in it and what's the root? (Almost all Hebrew words have, at their core, a three-letter word. This word has five letters, only one of which I could tentative parse as a prefix -- incorrectly, as it turned out.)

That led us to Wikipedia, which says it's not of Hebrew origin and also says that the mishna understands it as an acrostic of three other words. Wikipedia doesn't say where it says that, so I tried Google, which told me that sha'atnez is discussed in Kelayim 9:1. It is, but the Hebrew there doesn't use that word. So that led me to start to ask the question on Mi Yodeya, where just about all Jewish questions get good answers, but after typing the title I saw a suggested match here, which points to a little farther down the page to Kelayim 9:8, where I found my explanation. Excellent; my question was already answered before I asked it.

So today I made my first-ever Wikipedia edit, to add that citation. (It was an anonymous edit because it seems like my usual account name is already in use but the "lost password" email hasn't come back yet. So maybe it's somebody else or maybe their server is slow, but I'd kind of like to find out if I already have an account there before I use a non-standard name that I may not remember. Demonstrably, I don't log in there often.)