palace car vs passenger car

palace car and passenger car both are nouns.

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

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

palace car: a passenger car for day travel; you pay extra fare for individual chairs
passenger car: a railcar where passengers ride

Other hypernyms of palace car include carriage, coach.

palace car (noun)	passenger car (noun)
a passenger car for day travel; you pay extra fare for individual chairs	a railcar where passengers ride