Related Clues:

• It simply isn't done
• Frowned-on practice
• After cheers, negative utterance forbidden
• Serious no-no
• Forbidden word of appreciation: I don't like that!
• Something not allowed
• Prohibition also involves sailor
• Sacred and prohibited
• Prohibited, or prohibit
• Something you can't do
• Forbidden, to society
• Key rings forbidden by custom
• Socially forbidden
• Frowned upon
• Bill ducks a subject to be ducked