buffet car vs diner

buffet car and diner both are nouns.

Word	Noun	Adjective	Verb	Adverb
buffet car	Yes	No	No	No
diner	Yes	No	No	No

As nouns, buffet car and diner are synonyms defined as:

Other synonyms of buffet car include dining car, dining compartment.

buffet car (noun)	diner (noun)
a passenger car where food is served in transit	a passenger car where food is served in transit
	a restaurant that resembles a dining car
	a person eating a meal (especially in a restaurant)