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.

---

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.

---

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

---

Red Flag ² British  

noun

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

---

Etymology

Origin of red flag¹

First recorded in 1770–80

Origin of red-flag²

First recorded in 1880–85

Example Sentences

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

That should be a big red flag, and it bears discussing.

From MarketWatch • Apr. 6, 2026

Additionally, the double bottom breakout above a $436.99 pivot unraveled very quickly, a red flag as we know the best breakouts tend to work out right away.

From Barron's • Mar. 26, 2026

The next week the squadron won the red flag, and Lieutenant Scheisskopf was beside himself with rapture.

From "Catch-22" by Joseph Heller