muggy
Mary Anne noted in passing recently that it was muggy in Chicago, and I realized that though I've known the word all my life, I didn't know where it came from.
Turns out (according to MW11) that it's from the dialect word mug, meaning “drizzle.” So I guess muggy originally meant drizzly rather than humid.
While I'm here, I like the phrasing of MW11's definition of muggy: “being warm, damp, and close.” There are relationships that could be described that way.
And it puts me in mind of other three-word sets, like “fast, cheap, and out of control,” but maybe that's a topic for another day.