How to Say "Not Good" in Japanese

よくない

yokunai

To say "not good" in Japanese, use よくない (yokunai).

よくない is often used to say that an action or habit is bad for your health or goes against social standards.

Which one should you use?

ダメ is an informal way to say not good, often used to say something is not allowed or won't work.

よくない is the plain form. In polite conversation, use よくありません (yoku arimasen) or yoku nai desu.

It is pronounced yokunai.

The word ダメ (dame), used for 'not good' or 'no good', is thought by some linguists to have originated from the word for 'dam' or 'embankment', referring to a place where water stops flowing.
The adjective いい ('good'), which forms the basis of よくない, is one of the few words in Japanese that changes its root completely when negated, shifting from い to よ.
When someone says よくない in a romantic context, it can be used as a playful or flirtatious way to suggest that a certain behavior is 'naughty'.

間食はよくない。
It is not good to eat between meals.
This sentence says snacking between meals is よくない.
Tatoeba #183705 by small_snow, translation #20828 by Zifre
タバコは健康によくない。
Smoking is not good for one's health.
Here 健康によくない means not good for your health.
Tatoeba #203422 by bunbuku, translation #854259 by Swift
太りすぎることは健康によくない。
Becoming too fat is not good for one's health.
This sentence also uses 健康によくない to say overeating harms your health.
Tatoeba #197128 by KK_kaku_, translation #34310 by Dejo
この商品の品質は良くないです。
The quality of this product is not good.
彼の態度は悪いです。
His attitude is not good.
この映画、全然ダメだった。
This movie was totally not good.
これって悪くないと思うけど。
I don't think this is bad.
6 more sentences on Tatoeba

Hiyori and Hiroto are discussing a plan to go out in the rain.

陽葵 Himari

外は雨だから、今行くのはよくないよ。
Soto wa ame dakara, ima iku no wa yokunai yo.
It's raining outside, so it's not a good idea to go now.
大翔 Hiroto

そうだね。じゃあ、後で行こうか。
Sou da ne. Jaa, ato de ikou ka.
You're right. Shall we go later then?
陽葵 Himari

うん。急いで行くのはよくないと思う。
Un. Isoide iku no wa yokunai to omou.
Yeah. I don't think rushing is a good idea.
大翔 Hiroto

分かった。ゆっくり準備しよう。
Wakatta. Yukkuri junbi shiyou.
Got it. Let's take our time getting ready.

Sources

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