Taboo

NONO

Think of a casual way to say something is absolutely not allowed.

"Taboo" is a word for something that’s forbidden or socially unacceptable, which directly matches the meaning of "NONO." The answer plays on the idea of a strict rule or something you shouldn’t do—like saying "no, no" to emphasize prohibition. It’s a straightforward clue where the definition hints at the answer without any hidden wordplay or tricks.