[Nyororin]

The question you`re asking is fundamentally the question that most linguists in Japan ask... And cannot answer.

The fact is, the exact origins of most of the Japanese language is a mystery. The roots of specific words can sometimes be traced, but in general, the older the word the harder it is to be sure... And there are a LOT of theories out there. In the end, it comes down to a lot of guesswork, so reaching a consensus is hard to do.