What happened to original, pre-Kanji, Japanese words?

Question

Some of the most common words in Japanese seem to have their origin in Chinese:

会議、日本、世界、先生、。。。

The evidence for this is, as far as I know, the fact that these words are written with characters, whose on-yomi is used to read that particular word.

Further evidence is that there usually is a synonym or an archaic form, that is written using characters whose kun-yomi is used:

会議　＝　出会い　 日本　＝　八洲　（やしま）according to tangorin.com

I imagine that these words were used by the Japanese before the introduction of Chinese characters to Japan.

However, some words do not have this form:

世界　＝　？　 先生　＝　？

How did the Japanese folks say these things before the introduction of Kanji and what happened to these words?

Answer 1

Your question is too broad to give a specific answer, so I'll try to give you a few pointers instead.

Given how early in Japanese history kanji were introduced, compounded with the fact that there was no writing system in Japan prior to their introduction, we're very much delving into the realm of conjecture.

I imagine that some words simply fell out of use, especially among the (newly) literate upper classes who started to use the prestigious new kanji-based words. In other cases, kanji may have been adopted as 当て字 for the original word.

If you want to look into it further, I'd suggest researching 大和言葉 and 漢語, and possibly looking up research on the various dialects, some of which may retain words derived from an older, pre-kanji influence Japanese word.