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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

"We see the official holding the red flag which means the track was not safe but we also see that the train did not stop or slow down, causing the crash," Siam said.

From Barron's • May 18, 2026

Former Moto2 champion Johann Zarco was also taken to hospital after crashing out of the restart, which triggered a second red flag.

From BBC • May 17, 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

A man was waving them on with a red flag tied to a stick.

From "The Kill Order (Maze Runner, Book Four; Origin)" by James Dashner