This is a loose follow-up of my first question here on JLSE. I tried to check gogen-allguide.com and 大辞林, but couldn't find anything definitive. Unfortunately I don't know any other resources for checking etymologies for (native) Japanese words.

So, my question is: What is the etymology of 宵【よい】? My guess would be 夜(よ)日(ひ).


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Gogen Allguide and my dead-tree version of Sh­ōgakukan Kokugo Dai Jiten in JA mention that, in the Heian period and earlier, the terms for "evening, night" were somewhat specific, going in order:

  • ゆうべ
    Early evening
  • よい
    Late evening, early night: dusk
  • よなか
  • あかとき
  • あけぼの

I can't find anything definitive at present about the derivation of 宵. I do note, however, that 夜日 is a separate word in its own right, yohi: "night and day, day and night". So that's probably not the source of 宵.

I do see that the older kana spelling was よひ. I note also that 夕 of similar meaning has an older kana spelling of ゆふ. I wonder then if these two might be cognate, with よひ representing some kind of inflection. Or, possibly, よひ might be the noun stem form of a hypothetical verb よふ, consisting of 夜 "night" + ふ "suffix indicating iterative or continuous action, or ongoing change". That said, I can't find evidence of any such verb in my sources to hand.


The link to JSTOR that snailboat added above in a comment previously didn't work for me, possibly due to net congestion or server trouble. I have since read through that paper by J. Marshall Unger, New Etymologies for Some Japanese Time-Words. In it, he provides the following theory on page 40 for the derivation of modern 宵{よい}, ancient yopi (my additions in [square brackets] for clarity):

Because free native nouns in Old Japanese could begin with p but not r, the derivation of yopi 'evening twilight' is not as problematic as that of yoru, though by no means certain. It was probably a relatively late reduction of a whole phrase such as *yo pikari 'night shining', with the same *yo 'night' morpheme. According to pJ [proto-Japanese] non-final mid-vowel raising, an ancient compound of the form *yo-pi would have yielded OJ [Old Japanese] *yupi, not yopi, and OJ pi 'sun, day' was not used for 'light'.

I'm not sure what pJ non-final mid-vowel raising is beyond the summary provided by Unger (apparently outlined in more detail in a separate paper by Frellesvig and Whitman in 2004), but from the context of Unger's paper, I find myself unconvinced—there are OJ terms that don't seem to exhibit this purported yo- > yu- shift. I'm also unconvinced that pikari would shorten to just pi, given that in all other contexts that I'm aware of, the shortest form is pika, though I am certainly open to some other term being the cognate source for the -pi in yopi.

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    @Earthliŋ, Footnote 10 on page 40 of the article notes OJ *pwi 'fire; light' is a B-type* [i.e. 乙類] syllable. Unger also romanizes 甲類 i as i and 乙類 i as wi to make that distinction. So his rendering of yopi would imply 甲類 for pi here, and as such, 火 as an 乙類 would not be a likely candidate for reconstruction. Commented Jun 2, 2014 at 18:59
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    As a side note, an additional reason for why I find yo pikari to be an unlikely source for yopi is that, in my own poking around in etymologies, ancient Japanese roots all appear to be, at most, two syllables. Pikari is the stem of verb pikaru, which itself might be decomposable as a compound of pi "sun, sunshine" + karu "to borrow". Although Unger states that OJ pi 'sun, day' was not used for 'light', the Man'yōshū uses 日 in ways that suggest that 日 was indeed used to mean 'sunlight, sunshine', c.f. poem #995. My understanding is that the Man'yōshū counts as OJ. Commented Jun 2, 2014 at 19:10
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    Ran across this the other day, realized I'd used the wrong poem number. Shogakukan's 国語大辞典 entry for 日{ひ} with a sense of "the sun's shining or heat; sunlight" gives a reference to Man'yōshū poem #1995, not #995. Click the link for the text. Commented Oct 5, 2015 at 22:49
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    One more for you -- doing further research into what this hi phoneme might be, I stumbled across an obsolete reading of hi (ancient pi) for 間: 『「ひま(隙)」の古形。』, with the etymology at 隙【ひま】 suggesting that the modern word hima is a compound of this ancient hi + ma (間). Shogakukan gives a quote from the 日本書紀【にほんしょき】 using this reading and meaning, suggesting that this is a very old term. This seems to be a much better semantic match as a possible etymon for 宵【よひ】: 夜【よ】 + 間【ひ】 = "night + period of time between two things". Commented Oct 6, 2015 at 0:06
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    The 日本書紀 is written in 漢文【かんぶん】, with the relevant term appearing in the line 『乘間得脱逃入其國。』 (source text here on the Chinese Wikiquote). I did some googling as to how/why a 訓読【くんどく】 of hi would be used for the 間 character in the source text. This Chinese website that's a bit like Scribd has a PDF with some discussion of this, but going in an odd direction (that hi is mistaken). Scroll down to the bottom of page 4, just under the red "P2015". Commented Oct 6, 2015 at 0:17

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