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I noticed that there is this る coming up in 日{ひ}→昼{ひる} and 夜{よ}→夜{よる}. I haven't seen ひる and よる used a lot in Classical Japanese, so ひ and よ probably came first.

What is the role of this る? Does it have a meaning, or is it simply a homophone-avoiding filler like 田-んぼ and 葉-っぱ? Is it by any chance related to 雲/曇る?


{{pad}} 「日{ひ}→昼{ひる}」と「夜{よ}→夜{よる}」にはどちらも「る」が入っていることに気づきました。「ひる」も「よる」も文語ではあんまり見ないので、たぶん「ひ」と「よ」が元の形だと思います。

{{pad}} この「る」はどういう役割なんですか?意味があるのか、それとも「田ん」や「葉っ」のように、ただの同音異義語を避けるための語尾でしょうか?もしかして「雲{くも}→曇る{くもる}」の仲間ですか?

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I'm not sure if anyone knows the answer, but る must be some kind of bound morpheme rather than an independent word compounded with よ/ひ, because at the time these words had formed, Japanese words never began with /r/. It does seem that よ compounded (e.g. 夜中) but よる did not. – snailplane Jul 7 '14 at 12:55
Unger writes: "Perhaps the -ru of both piru and yoru should be compared to the -ru in the adjective root akaru- 'bright' (cf. aka 'red', *aka 'brighten; open' [reconstructed in Martin 1987]), which seems to have added an intensive or transient sense. (Recall that piru could specifically denote 'noon'.) Alternatively, piru and yoru might have been reductions of longer expressions ..." – snailplane Jul 7 '14 at 12:56
Shogakukan's big dictionary makes a similar suggestion. From their entry for 昼: 「よ(夜)」に対する「よる(夜)」と同じく、「ひ(日)」に「る」のついたものという。「る」は接尾語的なものか。 Part of me wonders if the る might be the usual intransitive / passive verb suffix る, where the resultant verb form nominalized somehow; that said, the expected nominalization pattern would be り, not る. At any rate, ひる and よる as nouns were already in common use by the mid-300s to late 700s, when the Man'yōshū poems were written. Examples here. – Eiríkr Útlendi Jul 7 '14 at 17:42
"I haven't seen the forms with る used a lot" I meant relative to Modern Japanese of course. Nobody would use よ as a noun by itself now, but that seemed to be common back then. – user54609 Jul 7 '14 at 18:53
One of the 語源説 for the entries in 日本国語大辞典 suggests ヨオル【夜居】 and ヒオル【日居】/ヒアル【日有】, which seems relatively reasonable. It also mentions ル as some kind of morpheme. – rintaun Jun 14 '15 at 0:01

I think that no one can give you a clear answer to the question at this time, because all of the words, ひ, ひる, よ, and よる have existed for a very very long time. It's just too difficult for present people to find out the origin of the four words.

As far as I know, the words ひる, よ and よる were already common words for daily use in the Heian period (794 - 1185). I think I can say so because emakimono (絵巻物) written in the Heian period contain those words, and they are used in writings which describe their daily life or something not special. For example, all of the three words are used in Genji Monogatari Emaki(源氏物語絵巻). And other emakimono, such as Shigisan Engi Emaki (信貴山縁起絵巻) etc, contain some of them. The words were used as a word or a part of a compound word such as ひるつかた, みじかよ etc. (Those words which I saw were written in hiragana in the emakimono).

The word ひ meaning "daytime" (not the word ひ meaning sun, date, time or weather here) seems to be used in The Tale of the Heike (平家物語) and Kojiki (古事記). (I've not seen the reliable photos of them, so I don't know what character is actually used for the word in them.)

All of the words ひ, ひる, よ and よる are kunyomi (訓読み). And they all were born in the old enough time we can't (or almost can't) trace the origins now. Thus, it is very difficult to find out which word was born first and their grammatical compositions.

There is another Japanese word, Kami (神), which also already existed and was used by Japanese people in the 8th century and is commonly used now. Kami is actually very different from God, but Kami is generally translated as God in English. Anyway, Kami has been one of very important words for many Japanese people, maybe somewhat like the word God in English. So, not a few people have seriously and diligently researched the origin of the word Kami for a very long time. However, no one has succeeded in finding the perfect answer so far. A convincing view on it still doesn't exist. So, we don't know the origin of the Japanese word Kami etymologically. I guess that finding the origin of the る in ひる or よる is more difficult than finding the origin of the word Kami, because they are more ordinary words.

About which word is first, a Japanese linguist, Susumu Ōno (大野晋), wrote an interesting thing in a book called 『日本人の神』.


[歌牟鵝可梨]{か・む・が・か・り}(神がかり) (神代紀上)

[伽牟伽筮能]{か・む・か・ぜ・の}(神風の = 伊勢にかかる[枕詞]{まくら・ことば}) (書記歌謡八)

このように、カミ(神)のミはカミだけの独立語では mï 。カミを含む熟語では mu である。


I don't know if this is true or not, but, according to his this knowledge, it might be possible that ひる was an older word than ひ and よる was an older word than よ if the words ひる and よる were composed of multiple words. Of course, it can't be certain (at least for now), though.

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I’m not a grammarian, and I cannot explain well how る in 語る、喋る、投げる、変える、帰る、照る、降る functions as the flexional form of the verb. But る of 昼(ひる)and 夜(よる)is different matter from, and irrelevant to the 語尾変化 - flexion of the tail of Japanese verbs.

日 and 昼 are different words though their meanings look similar in English (day and daytime, or noon), while 夜 (yo) and 夜 (yoru) are same in the meaning.

What I’m saying is I don’t find any specific meaning and reason as their own in る in 昼 and 夜 (yoru) in terms of etymology. Perhaps it’ll be just a coincidence.

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This really does not answer, or even address the question, which is about etymology in the Japanese language. And it significantly confuses the (irrelevant) issue of kanji (which is about words in the Chinese language), and also uses a strange concept of "meaning", which seems to be about the English language. – Brian Chandler Jan 12 at 4:38
You say the qustion is about etymology. I wish to meet anyone who can provide etymological background of る in 昼 and 夜. It's like trying to scoup the moon reflected on the surface of water. Meaning of two defferent word is very important to explain that they are not of the same origin. Couldn't you understand that? Anyway,why don't you give your own answer before commenting other's answer, and possibly down-voting it. – Yoichi Oishi Jan 12 at 5:25


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This cannot possibly answer the question as 1) hiru, yoru have never been verbs, and 2) what you're describing is a modern phenomenon. – jogloran Jan 12 at 4:37

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