smoking car vs passenger car

smoking car and passenger car both are nouns.

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

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

Other hypernyms of smoking car include carriage, coach.

smoking car (noun)	passenger car (noun)
a passenger car for passengers who wish to smoke	a railcar where passengers ride