How did 今ひとつ get its negative meaning?


The word 今ひとつ has the surface meaning "yet another, one more", but it seems to
be more popularly used to mean "not entirely satisfactory", for example:

> その薬の効果は今ひとつだった。  
>  The effectiveness of the drug was not up to scratch.

Where did this other meaning come from? Which meaning do speakers feel is the
more primary sense? My guess is that it progressed from "one more" to
"superfluous, unnecessary" to "not performing its duty".




At least in modern Japanese, いまひとつ no longer means "yet another". This phrase
now always means "(not terrible, but) not up to snuff" or "not really
(perfect)". デジタル大辞泉
[has](https://dictionary.goo.ne.jp/word/%E4%BB%8A%E4%B8%80%E3%81%A4/) an
example of "いまひとついかがですか", but this is something we might see only in older
novels.

According to [this article](https://kangaeruhito.jp/article/3586), the modern
いまひとつ is a relatively recent expression that only came into use in the 1950's.
At first, it was a [negative polarity
item](https://japanese.stackexchange.com/a/16060/5010) that was always
followed by 欠く, 足りない, 分からない, etc., indicating that only "one more piece" is
missing for perfection (or full understanding, etc). Later, this started to be
used without an explicit negation. So something like "one more piece" became
an ordinary no-adjective meaning "not up to scratch".

There are similar expressions such as もうひとつ, いま一歩, もう一息. These tend to be used
with some form of negation, but it's not a requirement. (Of course, もうひとつ also
means "yet another".) いまいち emerged in the 1970's as a colloquial/slang version
of いまひとつ, but it's now widely used in formal documents as well.

See also: [Why does いまいち have the meaning of "not
good"?](https://japanese.stackexchange.com/q/13503/5010)




At least in modern Japanese, いまひとつ no longer means "yet another". This phrase
now always means "(not terrible, but) not up to snuff" or "not really
(perfect)". デジタル大辞泉
[has](https://dictionary.goo.ne.jp/word/%E4%BB%8A%E4%B8%80%E3%81%A4/) an
example of "いまひとついかがですか", but this is something we might see only in older
novels.

According to [this article](https://kangaeruhito.jp/article/3586), the modern
いまひとつ is a relatively recent expression that only came into use in the 1950's.
At first, it was a [negative polarity
item](https://japanese.stackexchange.com/a/16060/5010) that was always
followed by 欠く, 足りない, 分からない, etc., indicating that only "one more piece" is
missing for perfection (or full understanding, etc). Later, this started to be
used without an explicit negation. So something like "one more piece" became
an ordinary no-adjective meaning "not up to scratch".

There are similar expressions such as もうひとつ, いま一歩, もう一息. These tend to be used
with some form of negation, but it's not a requirement. (Of course, もうひとつ also
means "yet another".) いまいち emerged in the 1970's as a colloquial/slang version
of いまひとつ, but it's now widely used in formal documents as well.

See also: [Why does いまいち have the meaning of "not
good"?](https://japanese.stackexchange.com/q/13503/5010)

