It's the same thing with “unsweet,” which has apparently become the universal term at food establishments when you want unsweetened tea. I’m in the American South, so I encounter this constantly.
But what the hell is “unsweet”? What does that even mean? Did they sweeten it and then somehow take the sweetness back out? Was it accomplished through evaporation? Reverse osmosis? Some sort of industrial-scale anti-sugar process?
“Unsweet” isn't a word.
So when I order, I specifically say, “unsweetened tea,” and the server inevitably responds, “Unsweet?”
“Gotcha.”
No. You got nothing. I said unsweetened.