traffic light vs stoplight

traffic light and stoplight both are nouns.

Word	Noun	Adjective	Verb	Adverb
traffic light	Yes	No	No	No
stoplight	Yes	No	No	No

As nouns, traffic light and stoplight are synonyms defined as:

traffic light and stoplight: a visual signal to control the flow of traffic at intersections

Other synonyms of traffic light include traffic signal.

traffic light (noun)	stoplight (noun)
a visual signal to control the flow of traffic at intersections	a visual signal to control the flow of traffic at intersections
	a red light on the rear of a motor vehicle that signals when the brakes are applied to slow or stop