It is?
It seems no one knows that but you.
Well, now you know!
I googled it, and it's not on the first page. Or the second.
Hmm.... Let's see. I googled "AC" and "Crti" and "init", and I didn't get a lot on those, either.
Yet, we still use them, and we all know what they mean, eh?
Use it if you want, I honestly don't care. However, in terms of utility, you'll likely have to explain the term every time you use it, which renders it a less than useful term.
I have used it a lot--I use it when I speak of initiative, and I find that people understand what it refers to.
"Are you intentionally trying to get this term accepted into gamer vernacular?"
No agenda here. It's just a word I use for initiative. I like it. I've used it for decades. It's as comfortable to me as saying "DEX" or "AC" or "Crit" or "THACO" and other like gaming-related words.
So, when I speak initiative, I use nish. It's a hell of a lot easier to type than the full word "initiative" or even the shorten "init" that you bring up.
When I'm not speaking of initiative, I don't use it.