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• red flag
  red flag

  noun

  the symbol or banner of a left-wing revolutionary party.
• red-flag
  red-flag

  verb (used with object)

  to mark or draw attention to for a particular purpose.
• Red Flag
  Red Flag

  noun

  a socialist song, written by James Connell (1852–1929), Irish political activist, in 1889

red flag

¹ American  

noun

1. the symbol or banner of a left-wing revolutionary party.

2. a danger signal.

3. something that provokes an angry or hostile reaction.

   The talk about raising taxes was a red flag to many voters.

4. Also called powder flag.  Nautical. a red burgee, designating in the International Code of Signals the letter “B,” flown by itself to show that a vessel is carrying, loading, or discharging explosives or highly inflammable material.

5. (initial capital letters) a war game the U.S. Air Force holds several times each year at Nellis Air Force Base, Nevada, to train personnel in air combat.

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red-flag ² American  

[red-flag] / ˈrɛdˈflæg /

verb (used with object)

red-flagged, red-flagging

1. to mark or draw attention to for a particular purpose.

   The department has red-flagged the most urgent repair work to be done.

2. to provoke the attention of; alert; arouse.

   The animal's refusal to eat red-flagged the keeper that something was wrong.

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adjective

1. of or relating to a red flag.

2. intended or serving to emphasize, warn, incite, or provoke.

red flag ¹ British  

noun

1. a symbol of socialism, communism, or revolution

2. a warning of danger or a signal to stop

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Red Flag ² British  

noun

1. a socialist song, written by James Connell (1852–1929), Irish political activist, in 1889

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Etymology

Origin of red flag¹

First recorded in 1770–80

Origin of red-flag²

First recorded in 1880–85

Example Sentences

That was a huge red flag for me that we had to dig deeper.

From Los Angeles Times • May 20, 2026

Another major red flag about the website, advocates say, is that the website directs people to unregulated pregnancy clinics.

From Salon • May 17, 2026

The incident happened at Station Corner and a red flag brought the session to a close.

From BBC • May 7, 2026

So this retreat is a bit of a red flag.

From Barron's • May 4, 2026

The National Weather Service had issued a red flag warning for the Sierra Nevada range today, as they did almost every other day in the fall.

From "Two Degrees" by Alan Gratz