passenger vehicle vs double-decker

passenger vehicle and double-decker both are nouns.

Word	Noun	Adjective	Verb	Adverb
passenger vehicle	Yes	No	No	No
double-decker	Yes	No	No	No

As nouns, passenger vehicle and double-decker are synonyms defined as:

passenger vehicle and double-decker: a vehicle carrying many passengers; used for public transport

Other synonyms of passenger vehicle include autobus, bus, charabanc, coach, jitney, motorbus, motorcoach, omnibus.

passenger vehicle (noun)	double-decker (noun)
a vehicle carrying many passengers; used for public transport	a vehicle carrying many passengers; used for public transport