Why do many adverbs end with ず?


A quick search on [jisho.org](https://jisho.org/search/*%E3%81%9A) reveals
that many of the first page results of words that end with a ず are adverbs. So
this type of adverb is common.

In fact, it's true (at least for these first page results) that a word is an
adverb if and only if the final ず is written in kana instead of being part of
the reading of a kanji.

This doesn't seem like a coincidence.

I know that ず was historically a negative conjugation (per [this
question](https://japanese.stackexchange.com/q/235)), but I can't really why
that would make it a common adverb ending.

Does anyone know why this might be the case?




I don't think so many adverbs with ず in Japanese adverbs but I find some
examples of Japanese adverbs with "ず" at the end of a word are;

Group A: ず means negative conjugation あいかわらず (as not changed) あしからず (do not
treat it as bad thing) おもいがけず (as not supposed) おもわず (as not supposed)

Group B: ず is a part of Mimetic word うずうず (itchy) ぐずぐず (tardily)

Adverbs are changed shape of verb. Above Group A is changed with negative form
of verbs.




I don't think so many adverbs with ず in Japanese adverbs but I find some
examples of Japanese adverbs with "ず" at the end of a word are;

Group A: ず means negative conjugation あいかわらず (as not changed) あしからず (do not
treat it as bad thing) おもいがけず (as not supposed) おもわず (as not supposed)

Group B: ず is a part of Mimetic word うずうず (itchy) ぐずぐず (tardily)

Adverbs are changed shape of verb. Above Group A is changed with negative form
of verbs.

