red light

¹ American  

noun

1. a red lamp, used as a traffic signal to mean “stop.”

2. an order or directive to halt an action, project, etc..

   There's a red light on all unnecessary expenses.

3. a children's running game in which players must stop when “Red light!” is called.

4. a signal of danger; warning.

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red-light ² American  

[red-lahyt] / ˈrɛdˈlaɪt /

verb (used with object)

red-lighted, red-lighting

1. Informal. to stop or deter by means of or as if with a red light.

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red light British  

noun

1. a signal to stop, esp a red traffic signal in a system of traffic lights

2. a danger signal

3. an instruction to stop or discontinue

4. 1. a red lamp in a window of or outside a house indicating that it is a brothel

   2. ( as modifier )

      a red-light district

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Etymology

Origin of red light¹

First recorded in 1840–50

Origin of red-light²

First recorded in 1895–1900

Example Sentences

You might not even notice it unless you first saw the red light shining on the sidewalk above a pair of nondescript black doors.

From The Wall Street Journal • Apr. 14, 2026

Even though insects and mammals are very distant relatives, both appear to have arrived at the same molecular strategy for sensing red light.

From Science Daily • Apr. 9, 2026

It was cold—the temperature settled in at 30 degrees—and blue and red light flashed on the wall of Quirky Books from a nearby surveillance tower installed by the police.

From Slate • Mar. 25, 2026

For investors, Wall Street’s optimism is a flashing red light, notes DataTrek co-founder Nicholas Colas, who flagged the FactSet report in his newsletter Monday, calling it, “the most disturbing graph we saw this entire weekend.”

From Barron's • Mar. 24, 2026

When he arrived it was nearly six o’clock, and the sun was setting full and warm, and the red light streamed in through the window and gave more colour to the pale cheeks.

From "Dracula" by Bram Stoker

Related Words

• traffic signal