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