On chat, Chocolate helped me find some examples of adjectives produced from verbs using the しい suffix. In the following examples, it appears to attach directly to the 未然形:

勇む  →  勇ま + しい
悩む  →  悩ま + しい
喜ぶ  →  喜ば + しい
妬む  →  妬ま + しい
呪う  →  呪わ + しい
慕う  →  慕わ + しい
好む  →  好ま + しい
好む  →  好も + しい
頼む  →  頼も + しい

But in these last two examples, there seems to be an extra inserted:

嘆く  →  嘆か + わ + しい
忌む  →  忌ま + わ + しい

I can't seem to find a dictionary entry for or わしい. What is this ?

1 Answer 1


The in these words is actually the 未然形 of the 継続の助動詞「ふ」, which historically attached to the 未然形 of other verbs. In this case, the combination of 嘆く and formed the verb 嘆かふ, and the combination of 忌む with produced 忌まふ. It is these words that combined with the suffix:

嘆かふ  →  嘆かは + し
忌まふ  →  忌まは + し

In modern Japanese, the becomes , and the classical 終止形 is replaced with the 連体形 しき, which loses its /k/ and becomes しい:

嘆かは + し   →   嘆かわ + しい
忌まは + し   →   忌まわ + しい

So as you can see, these words aren't really exceptions. Your list includes 呪う and 呪わしい, and that word can be explained in the same way. And in all of these examples, the suffix しい is attaching directly the 未然形 of a verb.

By the way, there's some interesting discussion in English of the auxiliary in this blog post on tumblr.

  • 3
    @summea See It’s OK to Ask and Answer Your Own Questions. I worked this out on the chat, and jkerian suggested I post it as a question anyway, so I did! :-)
    – user1478
    Commented Apr 9, 2013 at 23:22
  • 5
    The details on ふ are correct, but rather beside the point. Consider 叩く vs. 戦う. The later is simply tatak-a-fu > tatak-a-[w]u, via the same ふ. Similarly, 嘆く and 忌む are beside the point. It is verb 忌まう (formally 忌まふ) and 嘆かう (formally 嘆かふ) which correspond to adjective 忌まわしい (formally 忌まはし) and 嘆かわしい (formally 嘆かはし).
    – Dono
    Commented Apr 10, 2013 at 0:07
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    @Dono, a minor point, but I think you mean "formerly" instead of "formally" -- the ふ and は spellings are considered obsolete since the spelling reforms after WWII, and these aren't used in formal writing. They might still get used in poetic writing or in other deliberately archaic contexts, but I haven't run across them in modern formal contexts. Commented May 16, 2014 at 18:18
  • Just wanted to add a link for the 呪う example, which I needed to think about for a bit to understand. kobun.weblio.jp/content/%E3%81%AE%E3%82%8D%E3%81%B5
    – dainichi
    Commented Feb 5, 2021 at 7:52

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