I thought about the word wow a little while ago. I’m not sure why it came to me: I don’t recall being particularly surprised by anything today.
I didn’t think about it too long, because it seemed to me a pretty simple and natural interjection, not much more than an instinctive sound, like Oh, or ow!
But then I thought about whoa, which is obviously very similar to wow, not just in terms of how they sound, but how we use them, to express surprise.
Now whoa, I was pretty sure, was long used as a signal for horses to stop. This, dating from the middle of the 19th century, isn’t it’s oldest used though. It dates back to at least the early 17th century, and was used as a cry to call for attention, a variation on who (as in who’s there, or you who are over there!)
The use of whoa to stop a horse comes from ho, a general exclamation either of surprise, or to gain attention. And this is where we finally find a link between wow and whoa, as wow comes from an old Scottish exclamation of surprise, no doubt related to ho.
These are all very simple and pretty naturally-occurring words, but when you start to think about them, you realise there are lots of other related words and expressions. Like yo, which is surely related to whoa, and ho, and probably you too. And then there’s yoo hoo! This is probably related to yo ho, a nautical call for attention, but I imagine its common usage is more related to how much it sounds like you.
Which is enough to make you say, if not whoa, then wow!