Understanding the conjugation 危のう


> 「わかってる」
>
> くどいほどに念を押す少女に、苦笑して応じた。
>
> けれどフレデリカはその答えにこそ苦笑する。
>
> 「わかっておらぬ。……その時は、 **危のう** なったら無理をせず退くが良い」
>
> 見下ろした先、フレデリカはこちらを見ない。
>
> 「忘れておったのだ。──人はたやすく死ぬのじゃな。どれほど先を望んでいても」

86─エイティシックス─Ep.2 ─ラン・スルー・ザ・バトルフロント─〈上〉 安里アサト

I’m aware that the girl called フレデリカ is using Classical Japanese which is
different from modern Japanese. How should I understand the conjugation of
危のう? What kind of conjugation is it? Does this kind of conjugation have any
special meaning or nuance? Any similar examples?




That's ウ音便, and the explanation provided in [this
answer](https://japanese.stackexchange.com/a/24218/30454) seems difficult to
improve upon.

> 「ウ音便」, in the simplest terms possible, is the dropping of the "k" consonant
> from the 連用形 (continuative form) of i-adjectives.

あぶない → あぶなく → あぶなう → あぶのう

So, あぶなくなったら becomes あぶのうなったら and I think the sentence now makes sense to you,
doesn't it? As for why the ウ音便 is used and what effects are intended with the
use of an ウ音便 here, we can get a clue from the use of おらぬ.

For more on ウ音便, see these posts:

[～うございます - keigo い-adjectives](https://japanese.stackexchange.com/q/765/30454)

[いただきとう and ありがとう](https://japanese.stackexchange.com/q/91525/30454)

[Historical prospective of ウ音便 transformation (e.g. 有難く =>
有難う)](https://japanese.stackexchange.com/q/42890/30454)

