I've been watching Borgen lately, Denmark's own equivalent of The West Wing. It's in Danish of course, with subtitles, and I don't recognize much in terms of language, but I do know when characters are saying hello and goodbye. Hello is "hej" which sounds like "hi" and "goodbye" is "hej hej", which sounds like "hi hi". I always find this amusing because to my American ear it sounds like someone is giving an enthusiastic greeting to someone who is just walking out the door. Childish, I know.
But it did get me to wonder where our American "hi" comes from. It isn't British usage, or wasn't the last time I had occasion to check. Many years ago, on my first trip to England, I was trying to master the British public phone and the pips and the coins and kept hanging up on the person I was trying to call. I would get out "Hi--" and then the line would go dead. I was feeling terrible about it, she was the wife of one of my favorite professors, so there was that added anxiety, but when I finally got her, and apologized, she said, "Oh, I knew it had to be you." I asked how and she said that it was because I kept saying "hi." It narrowed the field to an American and we were vaguely expected.
So maybe this made it's way to us somehow from Denmark, skipping England altogether?
Well, there is a Middle English "hy, hey" which "hi" probably comes from, according to the Online Etymology Dictionary. But this is not exactly the meaning of hi today. Like "Hey!" today, "hi!" was a call to pay attention to something--"Look out!". "Hi" as a greeting is American usage. It's interesting that though no one seems to be able to tell us how "Hi" found its way to the Great Plains, they can tell us that the "first recorded reference is to speech of a Kansas Indian" in 1862.
Way to be both precise and maddeningly obscure, Online Etymology Dictionary.
The title of this picture on Wikipedia is: "Indians who broke out of their reservation in Indian territory & made a raid across Kan in 1879 & killed settlers near Great Bend & other places. , by Leonard & Martin"
No "Hi"s exchanged there, I'm thinking.
There's a long thread on the drifting meaning of the word "hey" here, which seems to have followed a similar trend from calling attention to greeting, although it keeps that first sense of exclamation better than "hi" did.