diner vs passenger car

diner and passenger car both are nouns.

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

As nouns, passenger car is a hypernym of diner; that is, passenger car is a word with a broader meaning than diner:

Other hypernyms of diner include carriage, coach.

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