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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

The kicker, which Calder admits in hindsight is a colossal red flag: He had to pay $12,132 to make the change.

From The Wall Street Journal • Apr. 29, 2026

That is always a red flag for me when I’m reading an OLC opinion.

From Slate • Apr. 9, 2026

"He never had a single red flag at all."

From BBC • Apr. 7, 2026

On Feb. 4, it broke above a five-month cup-base pivot of $149.89, but the breakout quickly fizzled—a red flag.

From Barron's • Apr. 6, 2026

As she spoke, she swung her lasso round and round, eyeing the flagpole that jutted out from the tower wall high above them, the Institute’s red flag rippling gently beneath it.

From "The Mysterious Benedict Society" by Trenton Lee Stewart