red flag

Từ điển WordNet v3.1 - WordNet Dictionary

noun

1. a flag that serves as a warning signal
- we didn't swim at the beach because the red flag was up
• Hypernyms:
flag, signal flag, alarm, alert, warning signal, alarum
2. the emblem of socialist revolution
• Hypernyms:
emblem, allegory
3. something that irritates or demands immediate action
- doing that is like waving a red flag in front of a bull
• Hypernyms:
annoyance, annoying, irritation, vexation