red light

plural red lights

1. A warning light, especially as a traffic signal indicating stop.

   We ran three red lights on the way to the hospital.

   1 more example

   Paddington [the GWR HQ] saw the red light, however, and the extension to Nantgarw was withdrawn on the G.W.R. agreeing "to lay down the narrow gauge [actually standard gauge as compared to broad gauge] from Didcot over the whole of their system in South Wales."

   1955 April, D. S. Barrie, “Railways of the Bridgend District”, in Railway Magazine, page 447

   Synonyms: stoplight, stop light

2. A sign of a brothel.

   Roxanne, you don't have to put on your red light.

   1978, Sting, “Roxanne”

3. idiomaticA denial to proceed a ruling out of any possibility.