Related Clues:

• It's a bad thing
• Admonishing utterance
• Scrubbed, as a space launch
• Something best avoided
• Deed to avoid
• 'Entry forbidden'
• Called off
• Something that's taboo
• Baby's taboo
• Not ready, in NASA-speak
• Failed, as a plan
• Tot's taboo
• Proscribed act
• Mission-scrapping phrase
• Smoking while pumping gas, e.g.