Related Clues:
- Forbidden expressions of gratitude and disapproval
- Rising cricketer gets pair? Not to be mentioned
- Both appreciation and disapprobation are forbidden
- Prohibited practice
- Not allowed cheers? I don't like that!
- Modern composer's rules of grammar: double negatives are a ___ ?
- (Something) forbidden
- Impossibility
- (Irrational) prohibition
- Something totally unacceptable (informal)
- Wrong numbers
- "The Sweetest ___" (Sade hit)
- Possibility that's not an option
- Something that must not be done
- Out of practice Customs won't allow it