We have a lot of ways to say greet each other, but let’s just stick with the basics, shall we?
It surprised me to find out that hello is very recent, only showing up in 1883, and gaining popularity because people decided they liked to use it to greet people on the telephone. It comes from a word we used to get people’s attention, hallo, which I don’t think I’ve ever heard in conversation. That word is also fairly recent, showing up in 1781 (anything with exact years attached to it has to be recent), although it had a variant, halow (no relation to hallow or hollow, by the way, although it did give us holler), that originated way back in the middle of the fifteenth century. Hallo itself comes from another word, holla (no, not as in “Everybody holla!”), which was a command to get people to stop before it morphed from “stop what you’re doing” to “stop and give me your attention” sometime in the late sixteenth century. Holla comes from the French word holá, which is basically the equivalent of “Whoa!”.
Hi first showed up in 1862 (man, what did people use to greet each other before then?). No one’s sure where it came from, but it’s possible that it’s a variant of a Middle English word, hy/hey, which was basically the same thing. It’s not related to hello even a little bit, another thing that surprised me.
Hey is relatively old, showing up in Middle English in the early thirteenth century. Back then it had a bunch of different variations with slightly different spellings and pronunciations, like hei and ai and heh, all of which was an interjection with a different connotation—one might mean sorrow, another might mean anger. Because if there’s one thing English needs, it’s emotionally specific words.
Wow. That was a quick one.