Growing up in Kansas (midwest US), greeting is/was Hi. Moved to (South) Georgia US when I was 12. Greeting here is Hey. Has a special sound with a southern accent (My Georgia history teacher was Ms. Ray, so I got to practice by saying "Hey Ms. Ray". It's not the same as in a sentence such as "Hey, what are you doing?" Reading the comments above re Native American words, I'm wondering if that IS connected.