In my understanding, the part of speech of a compound word is determined by its ultimate morpheme. (複合語の品詞は、後にくる語(形態素)の品詞によって定まります)

蒸す(V)+暑い(Adj) → 蒸し暑い(Adj)

持つ(V)+物(N)  → 持ち物(N)

and a verb in its -ず form can be roughly treated as an adverb.

食事をたいらげた     ate up a meal

食事を残らずたいらげた  ate up a meal completely (without any bit of remain)

Here comes the question. I find compound words ending with verb-ず have a variety of 接続, none of them are used as an adverb, e.g.

知らずしらずのうちに (resembles noun+の+うち)

役立たずな人 (resembles 形容動詞+な+人)

恥知らず者   (resembles イ形容詞+者)

How should I understand such a variety of 接続? and when to use which 接続?


  1. I saw the subtitle "役立たず共め" in an anime, saw there is an example sentence "恥知らずなことをする" in my dictionary, and therefore I came up this question.
  2. I found compound words ending with verb-ず pretty versatile; it can be an adverb (in 日本人を恥知らず呼ばわりする外国人を批判する), a na-adjective (in 恥知らずな噓をつく), or a noun I guess? (in 馬鹿で恥知らずの人間になる) These three sentences are found on the Internet.
  • 1
    it can be an adverb (in 日本人を恥知らず呼ばわりする外国人を批判する) -- 恥知らず is a noun here.. 「Noun+呼ばわり」です.. eg 「泥棒呼ばわり」「犯罪者呼ばわり」「嘘つき呼ばわり」「人殺し呼ばわり」... By the way, 嘘つき, 人殺し, 年寄り, 金持ち etc. are 名詞 that derived from 「XX+連用形」, too, just like 役立たず, 恥知らず, 行方知れず etc.
    – Chocolate
    Feb 9, 2019 at 6:02

1 Answer 1


If you already know the masu-stem of some verbs can act as a noun or na-/no-adjective, you can think these ず-words are almost the same except that negation is included as part of the word. That is to say, there are a few lexicalized ず-words that work as nouns or na-/no-adjectives. Just like non-negative ones, many ず-words have unpredictable meanings, and you have to learn them individually. 役立たず and 恥知らず are typical examples, and they can safely work as nouns, na-adjectives and no-adjectives.

Other examples:

  • 向こう見ず reckless
  • 親知らず wisdom tooth​
  • 医者要らず keeping doctor away
  • 水入らず en famille; private
  • 鳴かず飛ばず obscure; inactive; unsuccessful
  • 飲まず食わず without eating and drinking
  • 開かず (as in 開かずの間 locked/sealed room)
  • 寝ず (as in 寝ずの番 night watch)

This type of ず is integrated in a fossilized expression, and you cannot arbitrarily add or remove it. For example, 恥知り and 向こう見 mean nothing. (Well, 飲み食い happens to mean something a bit different...) New words are very rarely coined using this grammar, but おにぎらず is a fairly new buzzword made from おにぎり.

  • "the masu-stem (連用形) of some verbs can act as a noun or na-/no-adjective," It doesn't provide 連用形 of a verb used as a na-adjective in the link. Would you kindly provide some examples?
    – NoNames
    Feb 9, 2019 at 12:11
  • 1
    @NoNames Yes, "妹思いな兄", "物知りな先生", "何かと物入りな時期", "暑がりな人", "楽しみな旅行" and so on. お洒落な人 also falls into this category if we track the etymology.
    – naruto
    Feb 9, 2019 at 14:22

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