stoplight

• stop light

stop +‎ light

stoplight (plural stoplights)

1. (US) A traffic control signal, traditionally consisting of three lights, colored green, yellow/amber, and red, meaning proceed, prepare to stop, and stop, respectively.
2. A light on the rear of a vehicle that is activated when breaking; a break light.
   • 1973, United States. Department of the Army, Organizational Maintenance Manual (TM-9-2320-211-20)‎, page 2-52:

     The rear lamps are combined with the service stoplights and are contained in stoplight part and blackout marker light assemblies at the rear of the vehicle.

The two-word form stop light was initially more common, but its usage plateaued around 1950, whereas usage of stoplight increased continually since that year, overtaking stop light around 1970.

• traffic light
• traffic signal (US)
• robot (S. African)

• spotlight, toplights