駄目よ

don't

→ 駄目だ
phrase Rare #25,157
don't A firm but often gentle way to say that something is not allowed or must not be done. The よ adds emphasis; this form can sound feminine or gentle depending on the speaker and context.
JA: ここで写真を撮っちゃ駄目よ。
EN: Don't take pictures here.

駄目よ

No way!

— ラスト、コーション (2007)

ダイエットに専念しなくちゃ駄目よ

You need to focus exclusively on your diet.

駄目よ

No way.

— ウィッチ (2016)

しかしでは今晩だけひとつ駄目よ

But just one tonight is out of the question.

— 生きる (1952)

まだ駄目よ

Not yet!

— ロード・オブ・ザ・リング (2001)

そんな違法な事駄目よ

You can't do anything illegal like that.

— ラスト、コーション (2007)