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

She is the mother of four of the children traveling in the SUV she was driving when it was struck by another vehicle that was allegedly speeding and ran a red light.

From Los Angeles Times • Apr. 5, 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 some reason that red light was always a source of comfort to me, and many nights I fell asleep looking at it.

From "Bad Boy" by Walter Dean Myers

Related Words

• traffic signal