passenger car vs carriage

passenger car and carriage both are nouns.

Word	Noun	Adjective	Verb	Adverb
passenger car	Yes	No	No	No
carriage	Yes	No	No	No

As nouns, passenger car and carriage are synonyms defined as:

Other synonyms of passenger car include coach.

passenger car (noun)	carriage (noun)
a railcar where passengers ride	a vehicle with wheels drawn by one or more horses
	a railcar where passengers ride
	a machine part that carries something else
	a small vehicle with four wheels in which a baby or child is pushed around
	characteristic way of bearing one's body