red light

Noun

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.
   • Paddington [the GWR HQ] saw the red light, however, and the extension to Nantgarw was withdrawn on the G.W.R. agreeing "to lay down the narrow gauge [actually standard gauge as compared to broad gauge] from Didcot over the whole of their system in South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. (idiomatic) A denial to proceed a ruling out of any possibility.