There’s something out of kilter about the way we use the word “kilter.” The word’s first appearance in print was around 1600, and for about a century before that it was “kelter.” Both kilter and its immediate predecessor “kelter” mean “in good order or good condition.” But various dialects of English have had different meanings for “kelter” (or possibly different words entirely that sound the same). “Kelter” has meant money, it’s meant nonsense, and it’s even meant a rough cloth used for coats in northern England.
Even though there’s a “kelter” related to a kind of coat, “kilter” doesn’t have any connection to the “kilt” worn in Scotland. “KIlt” probably comes from old Scandanavian words like “kilte” (Danish), “kilta,” (Swedish), and “kilting” (Old Norse), all of which have to do with folding and tucking, as you would do if you were shortening, say, a robe. You’d do that if you were going into a fight or battle and thought you’d need your legs unencumbered, which seems to be the earliest usage of “kilt” — at that time it was more often used as a verb, as in “kilt your skirt.”
But back to “kilter” and what’s off kilter about it. Cosmologists puzzle about the imbalance in the universe between matter and antimatter — theoretically there should have been a balance between them at the time of the Big Bang, but nowadays there seems to be a great deal more matter than antimatter around. There’s something quite similar about “kilter” (well, maybe it’s a little similar): although it means “in good order,” it’s never used that way. Nobody ever describes something as “in kilter” — it’s always “out of kilter” or “off kilter.” There might be a citation of “kilter” being used in a positive sense somewhere, but I couldn’t find it and neither could Kagi (it’s a better search engine than Google). This imbalance, like the matter/antimatter mismatch, seems to go back for some time; the earliest citation for the older “kelter” in the OED is from 1643, and it ’s a negative usage, mentioning guns that are “out of kelter.”
And that’s not the only problem. Although we know that “kilter” is based on “kelter,” nobody has a clue where “kelter” came from or why it means “in good condition.” Like the origin of the universe, it’s simply a mystery.