pm215 Wrote:I mean that (as with any language) the spoken language is primary, and Japanese deals in words, not in individual kanji. So there is 注ぐ (to pour), and 注意 (caution), 注射 (injection), 注文 (order), and so on. You can assign a 'meaning' to the individual kanji based on looking at common themes in the meanings of the words they turn up in, but that's a secondary thing and not actually very important.
I would say that in the case of words formed from "on" readings, the written language is primary.
Going back 1500 years. . .
The Japanese spoken language exists, but without writing.
Then. . .
Chinese symbols (kanji) are imported and assigned to write Japanese words. The Chinese symbol meaning is matched to the Japanese pronunciation. For example "dog" is written 犬 and pronounced "inu". This is the "kun" reading.
A little later. . .
Many new words are formed in Japanese by combining kanji. In this case it is more efficient to use the short (mostly one syllable) Chinese pronunciations of the kanji. These are the "on" readings.
The new words formed from "on" readings would be chosen according to the meaning of the kanji as the pronunciations by themselves had no meaning.
Suppose we want to make a word for "shipyard".
This is a place where ships are created.
This is a 所 where 船 are 造.
造船所 (ぞうせんじょ)
So the word is formed by choosing kanji with appropriate meanings, combining them, and then using the pronunciation that results.
The examples you give above: 注意 (caution), 注射 (injection), 注文 (order), were probably formed in the same way, i.e. by choosing kanji with suitable meanings and then using the pronunciation that results, not the other way round.